But how can God be self-existent if ALL existence is His creation? Does/did God create Himself?
He's the absolute source of all existence. He's beyond existence. Transcendent. There was no existence until He spoke at the Divine Utterance, by which He created ALL.
What I'd say is that God is not within the bounds of created existence.
Even though I'd concur, you don't realize you are passively omitting the central fixture of creation, just as all others have for two millennia (and more, actually, since no world religion accounts for the creation of all, even in antiquity).
Existence by itself and absolutely considered is unbound, because it's not limited by generic and specific forms and particular instances of them (as would be indicated by the a of a being). God is not
an existent or a being; He just absolutely IS Existence/Being. What you have left over when you strip away all finite limitations from being is Being, and this is the Divine Nature (Ousia).
Again, while I concur, you don't realize the necessary demarcation that has passively been omitted from creation. I'll elaborate in this post.
What do you mean by ALL? And how does your Miahypostatic Theology come into play here?
This is where I begin to uncover what EVERYONE has omitted from the various competing historical formulations of God. The differences have been to compensate for what they all omit. It's quite simple, and the first inclination is to either include it in one's existing doctrine or insist it's already included somehow. It's not. That's where the Miahypostaticism comes in.
Again, existence by itself is essentially unconstrained and uncontained.
Then it should be depicted as such. It's not, though unintentionally so. God's Transcendence has historically been combined with the central fixture of creation. That's why I make the distinction, which is semantics to illustrate the reality.
It's not constrained and contained until it's 'bottled up', as it were, within formal properties and the particular beings that exhibit them.
And this is my point exactly. And if you're honest as I unveil it, you'll see the crucial nature of the truth I present to correct all historical error.
We need to be clear on what is meant by the term existence. If by it you mean the existing created order, then orthodox formulations have never claimed that existence contains God.
Yes, orthodox formulations have ALWAYS claimed such; but unwittingly and unintentionally, thinking they have represented creation and God in transcendence. They have not done so, and that's the central omission of creation that ALL views share; and why they require specifc reconciliation that abrogates them ALL in the process.
And in any case, "contains" would not really be the proper term to use. Nothing contains God, properly speaking.
Correct, which is why ALL views are in error and in need of reconciliation that abrogates them. This leaves us with a Miahypostaticism. A hypostasis is NOT a "person". Hypostasis was utilized to distinguish between ousia, and doesn't represent individuated sentient consciousnesses or personhoods in the human sense at all. Hypostasis is substance contrasted to essence.
The multiplied (manufactured, actually) hypostases was the substitute for not representing the creation of ALL, leaving God's inherent existence to have to be differentiated in such a manner to account for F/S/HS as one God. It was unnecessary and superfluous; the result of ignorance during formulation.
But that was a shared ignorance amongst all proponents of various formulations compensating for the same omission in different ways.
Western theology has maintained that God is pure Act of Existing, but this should by no means be taken to mean that existence (in any sense) contains Him.
But it does, because ALL views have not depicted creation to include all that it included. That's what leaves God "contained" by existence in ALL historical views, including a Dyohypostatic Trinity.
Not following... What truth is that?
The truth that God created ALL. The O/orthodox position has been that eternity IS God, because God is eternal and is somehow represnetative of eternity itself.
Let me begin... GOD CREATED ETERNITY, when/as He inhabiteth it. THIS is the central and shared omission of ALL views, and FOR which they are all compensating in some manner within their formulation.
Before the Divine Utterance, by which God created ALL; there was ONLY God. God alone is UNcreated. God inhabiteth eternity. God did NOT "inhabit Himself".
Eternity had an inception. A beginning. It's a realm of existence. Created. The eternal heavenly realm is created. God does NOT have His inherent existence as one ousia/three hypostases IN eternity. The three hypostases are to compensate for this omission of the central fixture of creation... Eternity of heaven.
God is an utterly transcendent ousia. Period. That's His inherent state. Essence. When/as He spoke/breathed His Logos and Pneuma, BOTH realms of existence were created ex nihilo (out of nothing) as His Logos and Pneuma proceeded forth/proceedeth ex Deo (out of Divinity) when/as He created.
"By the word of the Lord were the heavens made; and all the host of them by the breath of his mouth." Psalm 33:6
Heaven is a plural noun, and the third heaven is left off as creation. The first heaven is where the fowl fly. The second heaven is the vast celestial expanse of the cosmos as the natural universe. The third heaven is where Paul was caught up, and is the eternal heavenly realm. Eternity. Created. Inhabited.
God is transcendent to the created heavenly realm of eternity that O/orthodox AND heterodox views have confined Him to. And please don't engage cognitive dissonance to somehow insist other views have OR can include the creation of eternity. They don't and can't. They are ALL abrogated AS they are reconciled to the central truth, retaining ALL the necessary sub-tenets of Trinity doctrine while reformulating.
The Son is the earthly immanent Theanthropic prosopon (face/person; appearance/presence) of the heavenly immanent hypostasis (substance/subsistence) of the utterly transcendent ousia (essence/substance) that IS God.
The hypostasis is two-fold, with the Pneuma being God's omnipresence and the Logos being God's localized point of personAL presence; the Logos having divided asunder (separated for distribution) God's own Spirit out from (ekpoureuomai) God's own transcendent Self (Soul).
If by ALL you mean ALL existence whatsoever, then no, He didn't and can't create ALL. In particular, He can't create Himself.
But eternity is created, and ALL formulations resign and constrain God's inherent existence to be "in heaven, and from which He created". Tertullian and all the other formulators adopted this understanding. In the 13th century, St. Thomas Aquinas further delineated the detail of the "internal processions of the Son and the HS".
They weren't INTERNAL. God ex- (out from) -pressed His Logos and ex- (out from) -haled His Pneuma. And by this Divine Utterance, God inhabiteth eternity when/as He created it. All creation is external to God, though He filled it with His own Breath and Word from it's inception.
He created eternity as His everlasting abode. He tents there. We have the promise of having His Spirit indwell us to tent there with Him for everlasting.
But God's inherent ousia is NOT existence as is portrayed by ALL formulations. Existence was created, and He "formatted" Himself to condescend to inhabit eternity when/as He created it; the substance OF His essence being externalized at the Divine Utterance.
Since Spirit/Soul are conjoined and can only be divided asunder (merismos) by the Logos, God's externalized (two-fold) hypostasis (Logos/Pneuma) is conjoined to God's transcendent ousia. The ousia is co-inherent in the processions of the Logos and the Pneuma.
In the created heavenly realm of eternity, God is ousia and two-fold hypostasis (essence and substance). The Logos is NOT the Son until embodied in flesh. God is NOT a Father until the Son's begottenness is consumated within earthly-immanent creation.
The eternality of the Logos is the eternality of the Son. They're co-terminous. The Logos became flesh as the Son. Theanthropos. The internal Logos became the external Son. The Eternal Son. Fathered. Not just by internal generation, but by being procreated into the earthly-immanent realm.
The key is understanding the Rhema OF the Logos. Rhema is the thing spoken. The subject matter. The topic or content OF the Logos. Logos is the intelligent wisdom and pondered reason OF the Rhema; and IF there is outward expression, it's that expression whether written, spoken, or embodied.
The thing spoken was the entirety of God's transcnendent Divinity. God spoke forth His ousia as hypostasis. Mary's faith hypostasis believed upon that hypostasis within the Rhema of the Logos, and the seed of the Logos was conceived in her womb as the Theanthropic Son.
A second of three hypostases didn't hypostasize and enter the womb. The Logos was the spiritual insemination of life from the life of God's OWN transcendence.
Procession and conception are NOT inception, so the Son had no beginning; being co-terminous with the Logos.
I'm not sure how you can do that while at the same time avoiding either modalism or relegating two of the Divine Persons (the Son and Spirit?) to some sort of less-than-fully-Divine status.
I just did, above.

I've UNcontrived Trinity doctrine and included the central omission of creation while reconciling ALL other views to the truth for Theology Proper AND Cosmogony.
O/orthodox Dyohypostatic Trinity mistakes the externalized two-fold hypostasis and conjoined ousia as one ousia/three hypostases, and further designates a diluted sense of substance as persons. (And that is often perceived as multiple sentient consciousnesses. It's not, and can't be. A hypostasis is NOT an indicator of human-like personhood).
Arians mistake the procession of the Logos for a creative act in some manner. Unitarians mistake the conception of the Logos for a creative act in some manner. Sabellians (by whatever title) mistake the same sense of multiplied hypostases as Dyohypostatic Trinity, but as sequential or dynamic individuated manifestations instead of "persons".
Others mistake other subtleties, but ALL are compensating for the shared omission of the created of the heavenly realm of eternity. That's a HUGE omission, and the key demarcation of the initiation of creation by the processions of the Logos and the Pneuma. Now they've been turned into human-esque "persons" or "manifestations"; or have been relegated to being created at some point at procession or conception.
In the very specific manner I've depicted above, and with further copious exegesis from scripture; God is a Miahypostatic Tri-Unity. But more candidly... In a manner that encompasses His utter transcendence and BOTH created realms of existence, God is Tripartite. Spirit-Soul-Body of One Divinity. Pneuma-Psuche-Soma of One Theotes. And we are in His image.
Maybe the Lord is the Father, the word is the Son, and the breath is the Spirit? I dunno, seems a pretty good guess though.
Great guess. Your form of doctrine just can't and doesn't convey that literality. But neither can any other form of doctrine. All must be reconciled to the truth.
I don't think They literally speak/are spoken or breathe/are breathed. We're using anthropomorphic language to try to describe a Reality that our puny, finite minds can't even begin to fathom.
It was quite literal, just as scripture says. Our finite minds CAN fathom whatever the oida knowledge of the Spirit conveys to us. I've illustrated it above.
I'm inclined to say that only God is uncreated, but I'm not entirely sure.
Wow. How can you be unsure of that?
God created everything that is contingent--i.e. that might or might not exist.
Correct, and your form of doctrine doesn't and can't depict that.
Again, all contingent being is created by God. If the denial of its existence succeeds as a coherent thought, then God created it.
Yep, including eternity. That's been combined with God Himself.
(continued briefly)