In this section we address the truths that God has revealed about Himself.
Part 1: The Trinity
In the Symbol of the Faith, the Creed, we profess believe in One God, the Father Almighty, the Creator of heaven and earth and of all things visible and invisible. We also profess belief that Jesus Christ is One Lord, not two (as some would claim--the human Jesus as one person and Christ as another divine person). He is the only begotten Son of God. All others that become children of God are so by grace in time. Only the Son is begotten of the Father before all time. God the Father is unoriginate and thus is not from anyone. The Son and Spirit, on the other hand, are from God the Father, and are both Light from the Light and True God from the True God. Christ was begotten before all time, not made in or with time, and thus not created. By Him all created things were made. He and the Holy Spirit are of one Divine Essence with the Father.
Only Father, Son and Spirit are of Divine Essence, and all else that exists is created essence. Christ took on full humanity without giving up any of His Godhood. The Holy Spirit is also truly Lord and God, along with the Father and Son, and is the Giver of Life. Like the Son, the Spirit was brought forth from God the Father in eternity. Unlike the Son, the Spirit was spirated in eternal procession, not begotten. Scripture explains this in the Psalms that the Son is begotten as a word, and the Spirit proceeds as breath. This is of course "human language," but just as when we speak, the word and breath come out concurrently yet are and remain distinct, so also of the Word and Spirit of God from all eternity. The Son and Spirit are not "modes" or "manifestations" the Father, but rather are distinct persons or hypostases, who share of His own "God-nature" or Divine Essence. St. Gregory the Theologian tells us to think of Adam, Eve, and Seth. Eve proceeded from Adam and Seth was begotten of Adam. They both shared fully Adam's "Man-nature" or human essence, yet clearly are distinct persons from Adam.
Section 2: Essence and Energy
That which the Father, Son, and Holy Spirit share only among themselves, we call the Divine Essence or Divine Nature. This Divine Essence is the eternal "God-nature" that God the Father has of Himself and which He shares from all eternity with the Son and Spirit by bringing them forth from Himself, eternally begetting the Son and spirating the Spirit from all eternity. However, The Father, with the Son and Spirit, shares Himself with His creation via His eternal natural Energy, which we also call Grace (Grace here is not a created thing, but rather God Himself as He interacts with His creation).