Sermon on Trinity Sunday

by a Dominican friar

“Blessed be the holy Trinity and undivided Unity: we will give glory to him, because he hath shewn his mercy to us.”

These words, from the introit of the Mass, express well the spirit of today’s feast. Today is not principally a day for petition, or penance, or even thanksgiving, but rather for glorification. We are glorifying God for what He is in Himself: three divine Persons, one eternal God. “He hath shewn his mercy to us” in many ways, but in no greater way than this: that He has made known to us this mystery of His inner life.

Men can know the existence of God, simply from looking at the world around them — though in our times, unfortunately, our enemy has succeeded in confusing many people even about this fundamental truth. By looking at the things that God has made, as the Book of Wisdom and St Paul tell us, human beings can reach some knowledge of the Creator, the Lord of heaven and earth. No one can fail to reach this knowledge without a serious fault on his part, and so we do well to pray for those whose minds, today, have been confused by false arguments, and who do not have a firm belief even in the existence of their Creator.

But this knowledge of God that we draw from nature is, so to say, a merely external knowledge of God. Nature teaches us to know Him as One, and as all-powerful, but it teaches us nothing about His inner life. It is as if we opened an atlas and looked at the map of some foreign country which we have never visited. We might learn the size of the country, and whether it was near to or far from the others, but we would not thereby come to know the country itself. 

For this reason, God has supplemented the knowledge of Himself that we draw from nature with a far higher kind of knowledge, which is the knowledge of divine revelation. In virtue of divine revelation, we are no longer dependent on our own intellects, which are easily confused by our imaginations and our emotions, especially when we try to reason about the highest truths. By divine revelation, our minds receive from on high all the truths which God wills us to know, as the dry ground is watered by the rains. And the greatest of the truths that He makes known to us in this way is that He is the Blessed Trinity: Father, Son and Holy Ghost.

How the noblest of the pagan philosophers would have desired to be taught the truth about God by God Himself! But this was not granted to them. In divine providence, mankind had first to be instructed in the doctrine of monotheism: the fact that there is only one God, and that, as the psalmist says, all other so-called gods are really demons attempting to gain worship for themselves. So, for many centuries, the Jews were instructed by God that He is one: Moses taught them to recite the prayer, “Hear, O Israel, the Lord your God is one Lord.” In the revelation given to the Jews, there are certainly hints of the Blessed Trinity, which are easy for us Christians to see. For example, God says not “Let me make man to my image”, but “Let us make man to our image”. This is why we have an image of the Trinity within us, in our soul, our thought, and our love. Or again, the prophet Isaias heard the seraphim chanting not “Holy is the Lord”, but “Holy, holy, holy”. Or again, the personification of Wisdom, whom we read about in several of the books of the Old Testament represents, among other things, the Son, with the Father from eternity: “I was with him forming all things: and was delighted every day, playing before him at all times” (Prov. 8:30). Likewise, in other places in the bible, where we read of the Word and the Spirit of God, or the Spirit of the Lord, it is easy for us to see that the inspired writers are speaking of the Blessed Trinity: but this was not clear to the Jews. Their task was to preserve monotheism, the knowledge that there is only one God: and even that task was one that they accomplished only with difficulty.

It was only in the fullness of time, with the coming of Christ, that the mystery of the Trinity was made manifest. Yet even here, a wise order was observed. Our Lord, by His earthly life, revealed Himself as the beloved Son. In this way, He brought to light what was hidden in the Old Testament. He enlightened the minds of the apostles to know Him as God, without losing the monotheism which they had received from their ancestors. But as far as we can see from the Gospel, He did not speak much of the Holy Ghost until the end of His mortal life. It is only in His discourse at the Last Supper, after they had received the Holy Eucharist for the first time, that we find Him telling the apostles many things about the third divine Person, who had been, so to speak, left somewhat in the shadows until then. God was acting toward the human race as a wise teacher, who does not begin a new subject until his pupils have mastered the previous one.

In the history of the Church, also, we find a kind of image of this. Of course, the apostles preached the Blessed Trinity from the beginning, since — in obedience to Christ’s command — they were baptising believers “in the name of the Father and of the Son and of the Holy Ghost”. But the solemn definition of the Trinity came after the time of the apostles. At the Council of Nicaea, the first of the ecumenical councils, the Church used the word “consubstantial” to define the equality between the Father and the Son. At the second great council, in Constantinople, she solemnly taught that that the Holy Ghost is equal to the Father and the Son, by saying that He must be adored and glorified with Them. Not longer after this, the magnificent Athanasian Creed was placed into the Church’s liturgy, as the fullest and most perfect expression of the faith in the Holy Trinity.

Yet even though the Church, by her creeds, had so well expressed God’s revelation of Himself, something else was still needed. Since other mysteries — such as the Incarnation and the Resurrection — are celebrated by a special annual feast, it was fitting that the Christian people should be reminded of the greatest of all mysteries, by a day set aside each year simply to honour it. As an Englishman, I am happy to find that the first votive Mass of the Trinity was apparently composed at the end of the eighth century by Alcuin of York, the English monk who did so much to promote theology and the liturgy. This is the votive Mass which we still have in our missal today. But, although it became popular, this was not yet an annual feast of the Church; it was more a means of private devotion. Two hundred years after Alcuin, in Belgium, the diocese of Liege instituted a public annual celebration of the feast of the Holy Trinity, and this practice spread to other dioceses. The feast was not always celebrated at the same time: some churches kept it on the last Sunday after Pentecost, rather than the first one. In this country, its position was apparently fixed by the martyr St Thomas Becket, who had been consecrated archbishop of Canterbury on this day, the first Sunday after Pentecost. Finally, in the year 1334, more than five hundred years after Alcuin had composed the votive Mass, the Church of Rome began to celebrate the feast, and the pope extended it to the whole Church.

It seems that one of the reasons why this feast was introduced was because the number of saints on the calendar had multiplied. During the first millennium, there was quite a small number of saints on the calendar. When the number of saints’ days began to increase, it often happened that Sunday was given to the celebration of a saint. There was even a danger that in the end all the Sundays could have been taken over in this way. That was prevented by the practice of commemorating saints while still saying the Mass of the Sunday; but the Church desired that Catholics should be reminded of the main purpose of Sunday Mass, and of every Mass, by this special celebration to glorify the Blessed Trinity. And so this Sunday, especially by its preface, which will be used on all the “Green” Sundays of the year, serves to prepare us for the rest of the liturgical year, until Advent.

Much more than that, this Sunday serves to prepare us for that which lies beyond the earthly liturgy: the liturgy of heaven. To be in heaven means to see God as He is, and to see God as He is means to see the Blessed Trinity. The blessed, that is, see the three divine Persons; they see how the Word proceeds from the Father as the perfect image of His substance; how by the love of the Father and the Son, the Holy Ghost proceeds eternally; and how the Father, Son and Holy Ghost, while loving and knowing each other as distinct, are one only God. 

This is the happiness of heaven, but which begins in this life. Every soul in a state of grace has the three divine Persons within herself. Such a soul can enjoy Their presence whenever she wishes, beneath the veil of faith, until the shadows pass, and she sees her God as He is.