The doctrine of the Trinity is difficult and perplexing to us. Sometimes it is thought that Christianity teaches the absurd notion that 1+1+1=1. That is clearly a false equation. The term Trinity describes a relationship not of three gods, but of one God who is three persons. Trinity does not mean tritheism, that is, that there are three beings who together are God. The word Trinity is used in an effort to define the fullness of the Godhead both in terms of His unity and diversity.
The historic formulation of the Trinity is that God is one in essence and three in person. Though the formula is mysterious and even paradoxical, it is in no way contradictory. The unity of the Godhead is affirmed in terms of essence or being, while the diversity of the Godhead is expressed in terms of person.
Though the term Trinity is not found in the Bible, the concept is clearly there. On the one hand the Bible strongly affirms the unity of God (Deuteronomy 6:4). On the other hand the Bible clearly affirms the full deity of the three persons of the Godhead: the Father, Son, and Holy Spirit. The church has rejected the heresies of modalism and tritheism. Modalism denies the distinction of persons within the Godhead, claiming that Father, Son, and Holy Spirit are just ways in which God expresses Himself. Tritheism, on the other hand, falsely declares that there are three beings who together make up God.
The term person does not mean a distinction in essence but a different subsistence in the Godhead. A subsistence in the Godhead is a real difference but not an essential difference in the sense of a difference in being. Each person subsists or exists "under" the pure essence of deity. Subsistence is a difference within the scope of being, not a separate being or essence. All persons in the Godhead have all the attributes of deity.
There is also a distinction in the work done by each member of the Trinity. The work of salvation is in one sense common to all three persons of the Trinity. Yet in the manner of activity, there are differing operations assumed by the Father, the Son, and the Holy Spirit. The Father initiates creation and redemption; the Son redeems the creation; and the Holy Spirit regenerates and sanctifies, applying redemption to believers.
The Trinity does not refer to parts of God or even to roles. Human analogies such as one man who is a father, son, and a husband fail to capture the mystery of the nature of God.
The doctrine of the Trinity does not fully explain the mysterious character of God. Rather, it sets the boundaries outside of which we must not step. It defines the limits of our finite reflection. It demands that we be faithful to the biblical revelation that in one sense God is one and in a different sense He is three.