The Gospel for Trinity Sunday is the familiar story of Nicodemus coming to meet Jesus and their ensuing discussion of the new birth. The new birth is an important topic in itself, and the passage shows us how the new birth or regeneration is dependent upon divine initiative and grace. This Scriptural emphasis on divine action is different from many common interpretations which emphasize human action. In the discussion, we see the Holy Trinity permeating the whole process. So let us briefly look to the basic doctrine of the Trinity in the context of this passage about the new birth.
First, we see the origin in God the Father, Creator of heaven and earth. This origin is assumed by both Nicodemus and Jesus (John 3:1-3). Creation is rooted in divine love and grace, and the Father's goal for His human creatures is that they have eternal fellowship with Him; in other words, God desires the salvation of human beings. Even when they rebel against Him, He seeks their reconciliation.
Secondly, we see an emphasis on the work of Jesus Christ at the beginning and end of the Gospel passage (for example, John 3:2, 13-17). Christ's public ministry is the occasion that draws the attention of Nicodemus. As the discussion progresses, it becomes clear that Jesus is more than merely an unusual rabbi. He is also God the Son. He is the embodiment of the Father's desire to save human beings by offering them grace for a new birth, a deep spiritual transformation and renewal.
Thirdly, we see that the Holy Spirit is the invisible power working behind and through natural creation and human history (John 3:5-7). Through the external means of Word and Sacrament, the invisible Spirit comes like the wind, sometimes abruptly, sometimes gently. The Holy Spirit comes to revive sin-deadened souls. He comes to apply the love and the grace of the Father and the Son and offer new life.
Thus, we see that a familiar passage of Scripture proclaims the Holy Trinity although it does not use the term or develop formal definitions. As always, we must be careful in two respects. On the one hand, we must see the distinctive work of each divine person. On the other hand, we must not separate their work. They are one in purpose and in essence. In the words of the Athanasian Creed, "we worship one God in Trinity, and Trinity in Unity; Neither confounding the Persons, nor dividing the Substance."