If God is all omnipotent and can therefore do whatever he wants, why does he need a son?
The wording of this question highlights a misunderstanding about the Christian doctrine of God. God’s omnipotence, which is affirmed by the Christian faith, by no means excludes the Christian belief in the triune character of God, the belief that the one God is Father, Son and Holy Spirit.
1. Christians believe in the singularity and the uniqueness of God
Jesus message about God can be summarised: ‘God, the Father, the Almighty’. The biblical texts show that the belief in one God does not mean: we only believe in one God, not in two or three gods. Rather, it means that our God has shown to be so singular and so unique that he can intrinsically exist only once. Because a God who was constrained or even restricted by other gods would no longer be the almighty father. That which is to be the highest possible must stand alone and cannot have an equal… if God is not one, then there is none (Tertullian, Church father, ca A.D. 155 – ca 220).
2. God, the Father, the Son and the Holy Spirit
The shortest way of expressing the meaning of the Christian confession of the triune God is: one God in three persons. This confession does not say: 1 person = three persons, one God = three Gods, as this would be nonsense. The Athanasian Creed (which, however, is not from St Athanasius but is believed to have originated around the year 500) says:
‚we worship one God in Trinity, and Trinity in Unity; Neither confounding the persons nor dividing the substance. (http://www.sacred-texts.com/chr/athacree.htm)
Similarly, the Trinity preface says:
Who with your Only-begotten Son and the Holy Spirit
are one God and one Lord,
not in the unity of a single person,
but in a Trinity of one substance.
This confession of the triune God is a deep mystery which no created mind can discover or comprehend on his own. It is the mystery of an unfathomable and overflowing love: God is no lonely being, but a God who gives and communicates from the overflowing of his own being, a God who lives in the community of Father, Son and Spirit and who can therefore also gift and create community. Because he is life and love himself, he can be life and love for us. And so we are part of the mystery of God in all eternity. From eternity God has a space for mankind. Ultimately, the confession of the triune God is the exegesis of the sentence: God is love (1Jn 4.8.16b). That from eternity God is life and love is blessedness and gives hope to us human beings in midst a world of death and hatred. Through our faith we may know that the final and deepest reality is life and love and that through Jesus Christ in the Holy Spirit we have been given a share in this reality. (“Katholischer Erwachsenen-Katechismus” [Catholic Adult-Catechis b the German Bishops Conference], Vol 1, p. 85)