Spinoza's Ethics: I.P25:

God's essence is not distinct from existence, as its essence is existence. In contrast, modifications (affectiones) of substance, such as ourselves, go in and out of existence. Here, the essences of modifications are distinct from the existences of modifications. Further, the essences of modifications are not limited by duration. Earlier I discussed the concept of the virtual in which the essences of modifications inhere in contrast to the concept of the actual in which the essences come into and express God's existence as things. Spinoza's corollary articulates two forms of these things - as modifications of attributes or modes in which attributes are expressed. 

Deus non tantum est causa efficiens rerum existentiae sed etiam essentiae. 

Translated as,

God is not only the efficient cause of the existence of things, but also of their essence.

Demonstratio: Si negas, ergo rerum essentiae Deus non est cause adeoque (per axioma 4) potest rerum essentia sine Deo concipi: atqui hoc (per propositionem 15) est absurdum. Ergo rerum etiam essentiae Deus est causa. Q.E.D. 

Translated as,

If you might deny this, then God is not the cause of the essence of things and to such an extent (by A4) the essence of things can be conceived without God. But this (by P15) is absurd. Therefore God is also the cause of the essence of things.

Scholium: Haec propositio clarius sequitur ex propositione 16. Ex ea enim sequitur quod ex data natura divina tam rerum essentia quam existentia debeat necessario concludi et ut verbo dicam eo sensu quo Deus dicitur causa sui, etiam omnium rerum causa dicendus est, quod adhuc clarius ex sequenti corollario constabit.

Translated as,

This proposition follows more clearly from P16. For from that it follows that from given divine nature just as much the essence of things as their existence must necessarily be deduced and as I might say in a word in the same sense as God is called the cause of itself, so too should God be called the cause of all things. This will be established even more clearly from the following corollary.

Corollarium: Res particulares nihil sunt nisi Dei attributorum affectiones sive modi quibus Dei attributa certo et determinato modo exprimuntur. Demonstratio patet ex propositione 15 et definitione 5.

Translated as,

Particular things are nothing unless modification of God's attributes or modes by which God's attributes are expressed in a certain and determinate way. The demonstration is evident from P15 and D5.

Spinoza's Ethics: I.P24: Things Produced

This proposition, demonstration and corollary are fairly clear. I.D1 states "by cause of itself, I understand that whose essence involves existence, or that whose nature cannot be conceived except as existing." We then learn in I.D3 that only substance is conceived through itself and not through another, thus, substance is self-caused under I.D1. Then, in I.D6, we learn that God is a substance. Then in I.P14, we learn that, except God, no substance can be or can be conceived. All else is produced by God and all that which is not self-caused can be conceived as not existing. So, it would appear that when things involve existence, they are manifesting or expressing God immanently. The conceptual relationships of virtual to actual, energy to matter and potentia to Potestas are all useful in understanding the relationship of essence to existence.

Rerum a Deo productarum essentia non involvit existentiam.

Translated as,

The essence of things produced by God does not involve existence.

Demonstratio: Patet ex definitione 1. Id enim cujus natura (in se scilicet considerata) involvit existentiam, causa est sui et ex sola suae naturae necessitate existit.

Translated as,

This is evident from D1. For that whose nature (of course, considered in itself) involves existence, is the cause of itself and exists from the sole necessity of its own nature.

Corollarium: Hinc sequitur Deum non tantum esse causam ut res incipiant existere sed etiam in existendo perseverent sive (ut termino scholastico utar) Deum esse causam essendi rerum. Nam sive res existant sive non existant, quotiescunque ad earum essentiam attendimus, eandem nec existentiam nec durationem involvere comperimus adeoque earum essentia neque suae existentiae neque suae durationis potest esse causa sed tantum Deus ad cujus solam naturam pertinet existere (per corollarium I propositionis 14). 

Translated as,

From this it follows that God is not only the cause that things begin to exist, but also that they persevere in existing, or (so I might use a Scholastic term) God is the cause of the being of things. For whether the things exist or not, whenever we attend to essence of things, we learn that the same [essence] involves neither existence nor duration. So to such an extent the essence of things can be the cause neither of their existence nor of their duration but only God, to whose nature alone it pertains to exist (by P14C1).

Spinoza's Ethics: I.P23: Infinite Modes

Here Spinoza ties together the prior two propositions in this difficult transition from God and God's existence (prior to P21) to God's modes. If everything can be stated as substance (that which is in itself) and modes (that which is in another), somethings are not clearly in one or the other. In P21, Spinoza addresses the example of the idea of God in thought. On closer scrutiny, it is difficult to distinguish the attribute of thought from the seeming mode which is the idea of God in thought. He articulates this relationship between substance and mode as immediate or "immediately." In P22, Spinoza addresses the example of motion and rest (as a form of measuring) in extension. Again, it is difficult to separate the two. Importantly, modes are "conceived" while attributes are "perceived." He articulates this relationship between substance and mode as mediante or "mediating."

Omnis modus qui et necessario et infinitus existit, necessario sequi debuit vel ex absoluta natura alicujus attributi Dei vel ex aliquo attributo modificato modificatione quae et necessario et infinita existit. 

Translated as,

Every mode which exists necessarily as infinite necessarily had to follow either from the absolute nature of some attribute of God, or from some attribute measured by a measurement which exists necessarily as infinite.

Demonstratio: Modus enim in alio est per quod concipi debet (per definitionem 5) hoc est (per propositionem 15) in solo Deo est et per solum Deum concipi potest. Si ergo modus concipitur necessario existere et infinitus esse, utrumque hoc debet necessario concludi sive percipi per aliquod Dei attributum quatenus idem concipitur infinitatem et necessitatem existentiae sive (quod per definitionem 8 idem est) aeternitatem exprimere hoc est (per definitionem 6 et per propositionem 19) quatenus absolute consideratur. Modus ergo qui et necessario et infinitus existit, ex absoluta natura alicujus Dei attributi sequi debuit hocque vel immediate (de quo vide propositionem 21) vel mediante aliqua modificatione quae ex eius absoluta natura sequitur hoc est (per propostionem praecedentem) quae et necessario et infinita existit. Q.E.D.

Translated as,

For a mode is in another, through which it must be conceived (by D5), that is (by P15), it is in God alone, and can be conceived through God alone. So if a mode is conceived to exist necessarily and be infinite, it necessarily ought to be concluded or perceived as such by some attribute of God insofar as that same attribute is conceived to express infinity and necessity of existence, or (what by D8 is the same thing) eternity, that is (by D6 and P19) insofar as it is considered absolutely. Therefore, the mode which exits necessarily and is infinite, has had to follow from the absolute nature of some attribute of God, either immediately (about which see P21) or by some meditating measurement, which follows from its absolute nature, that is (by the preceding proposition), which exists necessarily and is infinite.

Spinoza's Ethics: I.P22: Mediating Modes

Commentators have devoted significant discussion to this proposition. Like the prior proposition, this proposition focuses on those areas which follow with attribute-like quality. Since an attribute is what is perceived as the essence of substance, these attribute-like areas share the characteristics of infinity and necessity. I have taken a novel approach here in translating words related to modificatio. Many translators use this word interchangeably with Spinoza's Latin word affectio and translate both as "modification." Some translators use the English cognates directly with "modification" and "affection." I don't think that the English sense of these words does Spinoza justice. Earlier, I commented that affectio is better rendered by "modification" as it gives the sense of substance being shaped. Here Spinoza uses modificatio which is relatively rare in the Ethics. In each of his uses, I believe that the term was selected for its sense of attempting to measure not modify. So what is he saying here? He is describing measurements such as motion or rest or any other characteristics which are fundamental to an attribute such as extension. The same measurements could be done within the attribute of thought such as the idea of God in the earlier proposition.

Quicquid ex aliquo Dei attributo quatenus modificatum est tali modificatione quae et necessario et infinita per idem existit, sequitur, debet quoque et necessario et infinitum existere. 

Translated as,

Whatever follows from some attribute of God insofar as it is measured by such measure that necessarily exists as infinite within that same attribute, must also necessarily exist as infinite.

Demonstratio: Hujus propositionis demonstratio procedit eodem modo ac demonstratio praecedentis.

Translated as,

The demonstration of this proposition proceeds in the same way as the demonstration of the preceding one.

Spinoza's Ethics: I.P21: Immediate Modes

The demonstration in this proposition is exceptionally difficult and unusual as such. First, the demonstrations typically employ what has already been proven. But the first reference to a prior proposition is related to attributes, yet introduces a new concept - that thought is an attribute. The specific identity of the attributes has not yet been established in Spinoza's typically rigorous build. Next, the Latin is vague because both the Latin words for thought (cognatio) and for idea (idea) are feminine. As Spinoza builds his first demonstration, translators experience enormous confusion and, in my opinion, are wrong here. The problems start with the sentence Verum quatenus ipsa ideam Dei habet, finita supponitur. In this sentence, translating the first half as "Indeed, insofar as it has the idea of God," "it" (ipsa) is clearly referring to thought rather than idea since the latter would be redundant. All translators agree. 

The second half of the sentence is where interpretations of "it" diverge in the attempt to translate what reads as "it is placed as finite." Almost all continue to make "it" refer to thought. However, this makes no sense at all. He has just clearly stated in the prior sentence that thought is an attribute and attributes are infinite. If this had been his rendering, Spinoza would have typically concluded "and this is absurd." But he didn't. He moves into an elaborate discussion to address the exceptional difficulty of a piece of an attribute - like idea within thought - that is not finite. So my translation is correct and focuses on a mode or a piece of an attribute which is not finite. This sets up an issue - all modes are not alike as those which follow from the absolute nature of an attribute (which is what this proposition is about) differ from those which do not follow from the absolute nature of an attribute. 

The rest of the first proof of his demonstration moves into complete unreadability by following the mistranslation. Most commentators throw up their hands and just skip the nuances of the demonstration. That is a shame because Spinoza explores a critical issue here of movement from the infinite to the finite. The next sentence employs the rarely utilized D2 with its specificity of finiteness and it becomes critical - bodies limit bodies and thoughts limit thoughts - as specific finite things within infinite attributes. So here we have the issue that a finite idea must be limited by another finite idea as a finite thought (as opposed to the attribute of thought). However, a close reading highlights this special category of modes that almost function with attribute-like characteristics, as they inhere in the nature of each mode within the attribute. Conversely, they can be conceived of as a special category within attributes that have modal characteristics. As a result, this liminal level appears to play an important role in moving from infinite to finite.

Omnia quæ ex absoluta natura alicujus attributi Dei sequuntur, semper et infinita existere debuerunt sive per idem attributum æterna et infinita sunt.

Translated as,

All things which follow from the absolute nature of any of the attributes of God must have always existed as infinite or through the same attribute are eternal and infinite.

DEMONSTRATIO: Concipe si fieri potest (siquidem neges) aliquid in aliquo Dei attributo ex ipsius absoluta natura sequi quod finitum sit et determinatam habeat existentiam sive durationem exempli gratia ideam Dei in cogitatione. At cogitatio quandoquidem Dei attributum supponitur, est necessario (per propositionem 11) sua natura infinita. Verum quatenus ipsa ideam Dei habet, finita supponitur. At (per definitionem 2) finita concipi non potest nisi per ipsam cogitationem determinetur. Sed non per ipsam cogitationem quatenus ideam Dei constituit; eatenus enim finita supponitur esse : ergo per cogitationem quatenus ideam Dei non constituit, quæ tamen (per propositionem 11) necessario existere debet. Datur igitur cogitatio non constituens ideam Dei ac propterea ex ejus natura quatenus est absoluta cogitatio, non sequitur necessario idea Dei (concipitur enim ideam Dei constituens et non constituens). Quod est contra hypothesin. Quare si idea Dei in cogitatione aut aliquid (perinde est quicquid sumatur quandoquidem demonstratio universalis est) in aliquo Dei attributo ex necessitate absolutæ naturæ ipsius attributi sequatur, id debet necessario esse infinitum; quod erat primum. Deinde id quod ex necessitate naturæ alicujus attributi ita sequitur, non potest determinatam habere existentiam sive durationem. Nam si neges, supponatur res quæ ex necessitate naturæ alicujus attributi sequitur, dari in aliquo Dei attributo exempli gratia idea Dei in cogitatione eaque supponatur aliquando non exstitisse vel non exstitura. Cum autem cogitatio Dei attributum supponatur, debet et necessario et immutabilis existere (per propositionem 11 et corollarium II propositionis 20). Quare ultra limites durationis ideæ Dei (supponitur enim aliquando non exstitisse aut non exstitura) cogitatio sine idea Dei existere debebit; atqui hoc est contra hypothesin; supponitur enim ex data cogitatione necessario sequi ideam Dei. Ergo idea Dei in cogitatione aut aliquid quod necessario ex absoluta natura alicujus attributi Dei sequitur, non potest determinatam habere durationem sed per idem attributum æternum est, quod erat secundum. Nota hoc idem esse affirmandum de quacunque re quæ in aliquo Dei attributo ex Dei absoluta natura necessario sequitur. 

Translated as,

Conceive, if it is possible, (if indeed you deny [it]) something in some attribute of God that follows from absolute nature itself which may be finite and may have a determinate existence or duration, for example, the idea of God in thought. But thought, since it is placed as an attribute of God, is necessarily (by P11) infinite by its nature. Indeed, insofar as [infinite thought as attribute] itself has the idea of God, it [the idea of God] is placed as finite. But (by D2) a finite [thought] is not able to be conceived unless it [a finite thought] is limited by [a finite] thought itself. But not by [infinite] thought [as attribute] itself insofar as it [infinite thought as attribute] constitutes the idea of God, but so far as it [a thought] is placed to be finite. Therefore, by [a finite] thought insofar as [infinite thought as attribute] does not constitute the idea of God, which nevertheless (by P11) [the idea of God] must exist necessarily. Consequently, there is [infinite] thought [as attribute] not constituting the idea of God and for that reason, from its [thought's] nature insofar as it is absolute thought, the idea of God does not follow necessarily (for it [infinite thought as attribute] is conceived as constituting and not constituting the idea of God). This is contrary to hypothesis. So if the idea of God in thought or anything else (in the same manner is anything assumed since the demonstration is universal) following in some attribute of God from the absolute nature of the attribute itself, it is necessarily infinite. This was the first thing.

Next that which follows from the necessity of the nature of some attribute, can not have a determined existence or duration. For if you would deny this, let a thing be placed which follows from the necessity of the nature of some attribute, that is in some attribute of God, for example the idea of God in thought and let it be placed in some way that it did not exist or would not exist. Moreover, since thought is placed as an attribute of God, it must both necessarily and immutably exist (by P11 and P20C2). For this reason, final limits of the duration of the idea of God (for it is placed that for some reason it did not exist and would not exist), thought would exist without the idea of God. But this is contrary to hypothesis. For let it be placed that from thought given follows necessarily the idea of God. Therefore, the idea of God in thought or something which follows necessarily from the absolute nature of some attribute of God must follow that it cannot have a determined duration but is eternal through the same attribute. This noted follows that this same must be affirmed concerning whatsoever thing which is in some attribute of God which follows from the absolute nature of God.