So why do we often talk about God as one Person, for example Exodus 3:14, we are given that God is called 'I AM WHO I AM', so why is it possible to ignore that and assume that God is three Persons in 1? If God wasn't a singular being, Exodus 3:14 would surely read 'WE ARE WHO WE ARE', no?
I think part of the problem here is conflating terms.
The Athanasian Creed has this statement, "We worship one God in Trinity and Trinity in Unity, neither confusing the Persons nor dividing the Substance."
The Oneness of God is God's Being, His Substance, Essence, or in Greek
Ousia.
The Threeness of God is the Three Persons or in Greek
Hypostases.
The word
ousia refers to the fundamental
what or "is-ness" of a thing. A tree has tree-ness, a rock has rock-ness. My
ousia is human-ness, humanity, I am a human being. Think of "being" as "is-ness", what a thing
is. That's what
ousia refers to.
The word hypostasis is an interesting one, but you can think of it as referring to "this-ness", the underlying, fundamental reality of something as a concrete, real, distinct
this.
As such we refer to Three Hypostases. That is to say, when we speak of the Father, we speak of the Hypostasis of the Father, that this One is indeed the Father, He is the Father of the Son. We do not mean merely that there is an external perceived distinction between the Father and the Son, we mean there is a real distinction--the Father is actually Father, the Father of the Son. The Son is actually Son, the Son of the Father. The Spirit is actually the Spirit, the Spirit of the Father and the Son. There is an actual, real distinction; because there is a real relationship between the Three.
And yet, we do not have three Beings, we have one Being. Because the Ousia of the Father, what the Father
is, is the same
what which the Son
is and
what the Spirit
is. The Father is God, the Son is God, the Holy Spirit is God--one God. Because the Being is one, undivided, absolute.
The Three are One. The One is Three.
And we do not mean here merely Being as "kind" as though the Father, Son, and the Holy Spirit are three examples of Divinity; in the same way that you, me, and that guy over there are three human beings. There are
not three Divine
Beings, there is one Divine
Being.
We say this by speaking of the Son's eternal generation from the Father, and the Spirit's eternal procession from the Father [and the Son]. The Son does not have being apart from the Father, but in and of the Father, eternally--the Son therefore is what the Father is. The Spirit, likewise, proceeding, is what the Father and the Son. The Son is the one and only God, indivisible and supreme, because He is what the Father is; and the Spirit likewise on account of what the Father is. And this from all eternity.
The Father is God. The one and only God.
The Son is God. The one and only God.
The Spirit is God. The one and only God.
Because the Three are the one and only God.
The Son is God because He is eternally
homoousios with the Father.
The Spirit is God because He is eternally
homoousios with the Father and the Son.
Homoousios is Greek meaning "same Being",
homo ("same") +
ousia ("being").
Thus there is one God, the Father, the Almighty Maker of heaven and earth, of all things seen and unseen. And in Jesus Christ, His only-begotten Son our Lord, eternally begotten of the Father, God of God, Light of Light, very God of very God, begotten not made, of one Being with the Father. And in the Holy Spirit, the Lord and Giver of Life, who proceeds from the Father [and the Son] who with the Father and the Son is worshiped and glorified.
One God. Worshiped in Trinity, Trinity in Unity, neither confusing the Persons nor dividing the Substance.
-CryptoLutheran