During this season of Advent, it is essential that we understand one of the Cardinal doctrines of Christianity; the Doctrine of the Trinity. The Christian doctrine of the Trinity is the doctrine that God exists as a unity of three distinct persons: Father, Son, and Holy
Spirit. Each of the persons is distinct from the other yet identical in essence. In other words, each is fully divine in nature, but each is not the totality of the other persons of the Trinity. This doctrine gives us logical affirmation for the Incarnation, the Atonement, and the Resurrection and allows us to be confident in the intellectual veracity of the hope that is within us.
My favorite analogy is explained by philosopher Peter S. Williams:
“…A musical chord is essentially composed of three different notes (to be a chord all three notes must be present), namely the first, third and fifth notes of a given musical scale. For example, the chord of C major is composed of the notes C (the root of the chord), E (the third from the root) and G (the fifth from the root). Each individual note is ‘a sound’, and all three notes played together are likewise ‘a sound’. Hence a chord is essentially three sounds in one sound, or one sound essentially composed of three different sounds (each of which has an individual identity as well as a corporate identity). By analogy, God is three divine persons in one divine personal being, or one divine personal being essentially composed of three divine persons. Moreover, when middle C (the root of the chord) is played it ‘fills’ the entire ‘heard space’. When the E above middle C is played at the same time, that second note simultaneously ‘fills’ the whole of the ‘heard space’; yet one can still hear both notes distinctly. When the G above middle C is added as well, a complete chord exists; one sound composed of three distinct sounds:” 
The Christian concept of God seems to be superior to the unitarian concept in that God, as the greatest conceivable being, must be loving rather than unloving. Love, however, reaches out to another person rather than centering wholly in oneself, as the very nature of love is to give oneself away. So if God is perfectly loving by His very nature, He must be giving Himself in love to another. But who is that other? Since God is eternal and creation is not, we can imagine a possible world in which God is perfectly loving and yet no created persons exist, as was the case without our space/time universe. So created persons cannot sufficiently explain whom God loves. Since God is a plurality of persons, as the Christian doctrine of the Trinity affirms, He can be in an eternal loving relationship without creation.
On the unitarian view God, however, God does not give Himself away in love for another; He is focused essentially only on Himself. Since God is essentially loving, the doctrine of the Trinity is more plausible than any unitarian doctrine of God.
“The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.” 2 Cor 13:14
1. Peter S. Williams, Understanding the Trinity, 2012.