If the Epistle and Gospel assigned to this unique feast do not seem to have much to do with the doctrine of the Holy Trinity, there is a reason for it. These passages were assigned long before there was such a thing as Trinity Sunday. Unlike Christmas, Easter, and Pentecost (which go back to the earliest centuries), Trinity Sunday was an invention of the late Middle Ages. When the Bishop of Rome, after some hesitation, made Trinity Sunday a universal feast throughout the Church, the English portion of the Church simply kept the same Epistle and Gospel which had always been used, even when the day was labeled "the Octave of Pentecost." So to find a good preaching text for Trinity Sunday, should we look elsewhere?
But is there any text of the Bible which does not contain this precious truth? While the word “Trinity” happens not to occur in Holy Scripture, we need look no further than the very first chapter of the very first book, “The first book of Moses called Genesis” (to use the title in our Authorized Version). There we read: “In the beginning God created the heaven and the earth.... And the Spirit of God moved upon the face of the waters. And God said...”
In those crisp and succinct words we have the whole doctrine of the Trinity before us. Here we learn that God is greater than all things, before all things, surpassing all things. We rightly call Him Father. But God is nonetheless present and active in His creation, invisible as the wind but far more powerful. Therefore we know Him as Spirit. The Hebrew word translated “Spirit” also means “wind,” and likewise means "breath." This "Spirit" of Genesis 1 is echoed both in the reference of the “mighty wind” which accompanied the Spirit on the first Whitsunday and to the "breath" with which Jesus breathed upon His disciples on the evening of the first Easter Day.
We must not overlook the significance of that little word “said” in the Creation account. Each creative act through the Six Days begins with “And God said.” In that simple verb, we learn “In the beginning was the Word, and the Word was with God, and the Word was God.” This “And God said” is what the Psalmist had in mind when he wrote “And He spake, and it was done; He commanded, and it stood fast” (Psalm 33:9).
This creative Word, by which the Father made all things at the beginning, was the very same Word which took on our very nature in Jesus Christ, God Incarnate. God's great Self-revelation which became perfect on Pentecost had been true all along. Trinity Sunday is a salutary reminder of how great a God we serve and adore. “O the depth of the riches both of the wisdom and the knowledge of God!” (Rom. 8:33).
Today's feast celebrates not an event but a dogma. Christmas, Easter, Ascension Day, Pentecost, and even All Saints Day are our annual reminders of the mighty acts of God in our world of time and space. But Trinity Sunday comes not as an anniversary but as a lesson-plan. We need to be instructed at least once a year that the One unique God, who demands our exclusive allegiance and worship, has existed from eternity as a unity of three persons, and so He will always be.
If this seems to be abstract and irrelevant to our lives here and now, we need to be reminded of one critical event in which the Trinity of the Father, th Son, and the Holy Ghost has profoundly touched each one of us. That critical event was our Baptism, when each Christian individual was washed and marked “in the name of the Father, and of the Son, and of the Holy Ghost.” This Dominical formula, found in Matt. 28:19, is absolutely necessary for a valid baptism to occur (along with, of course, the use of water). This is the only place in the whole Bible where the threefold nature of God is stated so precisely. Note carefully that there are not three “names,” but only One Name.
Our salvation (and this is the salvation of each of us, considered one at a time) is rooted in God's plan for our salvation. That plan was not merely an emergency measure which God contrived after man fell into sin; in the words of the psalmist, God's saving love for us is “from eternity, to eternity.” This proves to us that God is truly our Father, and has been our Father from before all time.
But at a certain moment in time (as time is measured by a clock!), God stepped right into our fallen world and became active on our behalf, to redeem and restore us, to defeat the powers of evil which enslave us, to re-establish His kingship in our hearts, our lives, and our world. That all happened when the Son of God, Jesus Christ, who is truly God the Son, was made man in Palestine.
This eternal God, who created us and redeemed us, is still present with us. This presence we call God the Holy Ghost. As the Holy Ghost or Holy Spirit, God penetrates and pervades all things. But most important for us, He applies to us now that God the Son has done for us long ago. He engrafts us into Christ and unites us to Him, so that even in our dull and unglamorous human existence is already shot through with the Divine life of God.
The Triune God, into whose glorious Name we have been baptized, thus reveals Himself to be both our Creator and our Saviour.