Answer: Trinity Sunday is the first Sunday after Pentecost to honor the Holy Trinity—the Father, Son and Holy Spirit. Although the word “trinity” does not appear in Scripture, it is taught in Matthew 28:18-20 and 2 Corinthians 13:14 (and many other biblical passages). The concept of the trinity can never be completely understood or rationalized, but it is clearly taught in Scripture. Understanding of all scriptural doctrine is by faith which comes through the work of the Holy Spirit; therefore, it is appropriate that this mystery is celebrated the first Sunday after the Pentecost, when the outpouring of the Holy Spirit first occurred.
On Trinity Sunday, the Christian Church ponders with joy and thanksgiving what the Father, Son and Holy Spirit have done to accomplish the salvation of sinful humanity. It is brought to remembrance how Christians should respond to the love God has shown us, praising Him and giving Him glory. We remember the Father as our Creator, the Son as our Savior and the Holy Spirit as our Comforter. Scriptural readings for the Trinity Sunday ceremony may include Psalm 8, beginning and ending with, “O Lord, our Lord, how majestic is your name in all the earth.” Second Corinthians 13:11-13 appeals to believers to aim for perfection and live in peace, ending with the prayer that the grace of Christ Jesus, the love of God and the fellowship of the Holy Spirit be with all, including again the commission Jesus left for believers in Matthew 28:16-20.
Today, Trinity Sunday is to explain, to the best of man’s ability, the clues written in Scripture to guide us to a fuller understanding of our triune God. The Father is God from the beginning (John 1:1); Jesus revealed Himself as equal to the Father in John 10:30, “I and the Father are one.” Together, they sent the Holy Spirit (John 14:26). “For there are three that bear record in Heaven, the Father, the Word and the Holy Spirit; and these three are one” (1 John 5:7-11).