The creed to which every Christian gives his allegiance begins with the words, “I believe in one God”. However, unlike any other religion under the sun, this one God is not the same as the one god claimed by non-Christian belief systems who also speak of one god. The God of Christians cannot be reduced to the philosopher’s "one" unmoved mover, or the "one" energy source behind all things. He is not the one god of the Gnostics, who speaks secrets to individuals so by those secrets they alone might have knowledge of what & who God is. He is not the one god of neo-Platonists, who is a great ruler and cares mostly about perfection and having his honor restored (this is the great error of western theology since the great schism of the 11th century). He is not the one absentee landlord god of the deists (this is one of the most popular versions of god in our day). He is not the summation of the whole universe into one great sea of spirituality (this is the other popular "one" god of our day). Instead of these kinds of "one" god, the God we know as Christians is one essence, in three persons, who makes His presence experiential to His creation by way of His energies (ergos-works).
The understanding of the undivided church is that there exists one God; meaning that there is no internal difference within the one God, He has one mind, one plan, one set of affections, one intention, and there is no division at all within Him. Yet, in a mystery, we find that He exists in three persons: the eternal Father who is the maker of all things visible and invisible; the Son, who is eternally begotten of the Father, meaning that there has never been a time when the Father was that the Son was not, & by whom the Father accomplishes all things; and there is one eternal Holy Spirit who is the same God and the author of life and has eternally proceeded from the Father. This means that there was never a time when the Spirit was not. This one God who exists in three persons in one godhead, and these three persons make up the one perfect community of love, light, and life whom we call the Trinity.
It is in this one community or Trinity that all things live and move and have their being. Thus, it is into life within that community that all humanity and creation is called. For this reason, every great Christian teacher has said that man cannot know himself unless he first knows the one God (no communion = no true humanity). It is for this reason that Holy Communion is the goal of creation and also the means of restoration for our divided creation. Therefore, the one God that we know as Christians desires above all things to have the whole creation intertwined within his godhead which we call the Trinity and that is what we call salvation. In short, our God is the one who loves love, He loves our love and who wants us to be inter-twined with Him. Consequently, each person of the Trinity is involved in the task or creating communion unto the ages of ages.
This also means that there can exist no difference of mind within the godhead. To us who live in America this means that God the Father is not primarily angry, and the God Son is not trying to block the Father’s anger from hurting us, and the Holy Spirit is not merely keeping the peace and putting the reunion together. That would be a divided mind within the Godhead, or divine schizophrenia. God the Father and God the Son cannot be of different interests. Instead, what we need to grasp as American Christians is what the patristic and apostolic church of the first millennium understood, and that is that our God is one community, has one love, and one mission, and it is to bring all things into Himself, and into His perfect and loving community which we call the Trinity. Our one God now calls mankind to freely enter into that community, because the Lord Jesus Christ has destroyed that which prevented us from entering in, which is the sin and death that mankind introduced into the world. Moreover, a day will come when that union will be consumated in time and space, and sin and death will be no more.
Christ has been raised from the dead, the firstfruits of those who have fallen asleep. For as by a man came death, by a man has come also the resurrection of the dead. For as in Adam all die, so also in Christ shall all be made alive. But each in his own order: Christ the firstfruits, then at his coming those who belong to Christ. Then comes the end, when he delivers the kingdom to God the Father after destroying every rule and every authority and power. For he must reign until he has put all his enemies under his feet. The last enemy to be destroyed is death. For "God has put all things in subjection under his feet." But when it says, "all things are put in subjection," it is plain that he is excepted who put all things in subjection under him. When all things are subjected to him, then the Son himself will also be subjected to him who put all things in subjection under him, that God may be all in all. 1 cor 15: 20-28
This one God, this one mind, and this one mission is the clear teaching of the bible, the apostles, the church Fathers, the ecumanical coucils, the creeds, and of the whole undivided church. It is to this foundational oneness of God (Trinitarianism) that the teachings of the church must return if we are to have the true God as our God.