The Persons of the Trinity are not three separate divine essences. They are co-equal and co-sharers of the one divine essence of God. Hence we say, in theological terms, the three Persons of the Trinity are three personal subsistences of the one, divine, essence. The word "Person" is unfortunately become overtaken by contemporary meanings, versus what the word meant when the doctrine of the Trinity was formulated from Scripture many, many, years ago.
I do not think one can deny the Trinity and be a Christian. It is an essential of the faith, and even the rules here at CF require Trinitarianism for anyone claiming to be Christian.
God is a simple and uncompounded spiritual
being. We can say the same by stating, God is a simple and uncompounded spiritual
essence.
Essence is that by which something is what it is, that is, its nature. The word
quiddity and its derivatives (e.g.,
quidditive) is sometimes used when discussing
essence.
Generally speaking,
essence and
being are interchangeable in most discussions of God. Some also use
nature and
essence interchangeably. But I try to avoid the use of the word
nature when discussing the doctrine of God, given the word’s heavy use when discussing the Incarnation. (As a rule one should avoid polymorphisms in theological discussions, but it is impossible for some topics, especially the Incarnation.)
While there is but one essence of God, there are three distinctly different modes of
subsistence in that essence, which we call
Persons. Unfortunately, as I stated above, in this modern era the word
person carries much more baggage than it did when the Trinitarian doctrines were being formulated. We tend to think of a
person as a separately existing beings from other beings. It is generally admitted that the word
person is but an imperfect expression of the idea of the Persons of the Godhead.
Hence, in God there are not three individuals alongside of, and separate from, one another, but three personal self-distinctions within the single divine essence, i.e., three modes of subsistence.
The word
subsistence is the subject of much philosophical debate, especially with respect to its connection to
essence and
existence. At issue is how
essence makes its existence known. Formally speaking,
subsistence is the means of individuation of essence with respect to existence. Less philosophically, subsistence is the means by which essence
exercises existence, or even more succinctly,
subsistence means something that really exists.
Thus we can say that the divine essence does not exist independently along with the three Persons.
The divine essence has no existence outside of and apart from the three Persons. For if the divine essence did, there would be no true unity, but a division that would lead into tetratheism.
John Feinberg notes:
“the three persons (hypostaseis / prosopoi) coinhering in the one divine nature (ousia) exist simultaneously with one another as distinct subsistences or persons. This means that the divine essence is not at one time entirely manifest as the Father (but not in or as the Son or Spirit), and then at another moment manifest exclusively as the Son, and yet again at another time solely as the Spirit. Rather, all three persons . . . exist simultaneously” (Src:No One Like Him).
God’s essence is common to the three Persons of the Godhead, and God’s essence is not communicated from one Person to another Person. Each Person partakes of the essence of God, possessing it as one undivided essence.
Portions of the essence of God are not divided up to be enjoyed by each Person, instead the whole essence is enjoyed by each, as “in him the whole fullness of deity dwells” (Col. 2:9, also John 15:16).
For each mode subsisting in the divine essence, each of the Persons has a
distinct mode of subsistence, such that we can say that the Son is not the Father, the Father is not the Son, and the Holy Spirit is not the Father nor the Son.
