In those days Jesus came from Nazareth in Galilee and was baptized in the Jordan by John. As soon as He came up out of the water, He saw the heavens being torn open and the Spirit descending to Him like a dove. And a voice came from heaven: You are My beloved Son; I take delight in You! - Mark 1:9-11 HCSB
God is undivided unity expressed in the threefold and equal nature of Father, Son and Holy Spirit. Being so far beyond our normal human experience, it is and will likely ever be a great and incomprehensible mystery.
Augustine of Hippo (AD 354-430) tried to illustrate the Trinity through the use of a psychological analogy. In his illustration, just as a person exists as one being with the three dimensions of memory, understanding and will; so also the Godhead exists as three Persons forming one.
Another common illustration is to consider that we exist as body, soul (mind, will and emotions) and spirit (that part that can experience God).
However, though we may strive to grasp it, we must conclude that it must be understood, not by intellectual speculation but by direct experience. This is not an unreasonable demand. Do we truly understand our spouses through intellectual assent to their heartbeat, respiration, the color of their eyes and hair, their height and weight or through emotional interaction and conversation? We must remember that the point of the Scriptures is not to increase our knowledge of but to improve our relationship with the Lord.[2]
The word “Trinity” as such does not appear in the Bible. It is a name that humans have applied to identify the concept that is clearly taught in the Scriptures. A recent preference is to refer to the Trinity as the “Triunity” in order to hopefully avoid a couple of misconceptions. One such error is the idea of tritheism. This concept over-emphasizes the distinctiveness of each person of the Trinity to the point where it becomes polytheism, which is a belief in three separate gods. This is not what Ransomed theology teaches for the Scriptures categorically state that the Lord is One and that there is no God but Him.[3]
Another mistake is to so emphasize the unity of the Godhead that that we begin teaching Unitarianism. Unitarianism ends up contradicting the clear teaching of the Scriptures by saying that only the Father is God and that Christ and the Holy Spirit are lesser and servile beings. That too is a complete heresy. Jesus did not equivocate but clearly stated His unity with the Father and that to see Him was to see the Father.[4]
[1] Trinity; by Andrey Rublyov; ca. 1411