Charles Ryrie defines the pre-existence of Christ as meaning that; “He existed before his birth”
Unity – There are not two or more gods.
Simplicity – There are not two or more parts in God.
Tri-Unity – There are three persons in the one God.
Baker Encyclopedia of Christian Apologetics - Trinity. Trinity simply means “Triunity.” God is not a simple unity; there is plurality in his unity. The Trinity is one of the great mysteries of the Christian Faith. The Trinity goes beyond reason but not against reason. It is known only by divine revelation, so the Trinity is not the subject of natural theology but of special revelation.
The Basis for the Trinity. While the word Trinity does not occur in the bible, the concept is clearly taught in the Bible. The logic of the doctrine of the Trinity is simple.
Two biblical truths are evident in Scripture, the logical conclusion of which is the Trinity. There is one God and there are three distinct persons who are God: Father, Son, and Holy Spirit.