Teach all nations:
baptizing them in the name of the Father,
and of the Son, and of the Holy Ghost.
—St. Matthew xxviii. 19.

The mystery of the Most Blessed Trinity is one of those wonderful truths of our holy faith which form the foundation of the Christian religion. He who does not believe in the Trinity cannot call himself a Christian; neither can any one be a Christian unless he is baptized in the name of the Father, and of the Son, and of the Holy Ghost. We are taught to make acts of profession of this mystery oftener than of any other. We do so every time we make the sign of the cross; and there are very few Catholics who do not make that sign more than once every day. Every one should know what is meant by the Trinity.

There is but one God, who is the infinite, eternal, almighty, all-wise, all-good, and all-just Being who created all things that exist.

But God, who is one in his Divine Being, is a Trinity in person. That is, he is three persons. These persons are named Father, Son, Holy Ghost. God is, then, Father, and he is Son, and he is Holy Ghost. These three persons are the same God. So, if there were three men praying to God, one praying to the Father, a second to the Son, and the third to the Holy Ghost, they would all be praying to the same God. How there can be more than one person in one being is a mystery to us, because we have no knowledge of any other being but God who has more than one person. But now this truth is revealed to us, we know, by our faith, which is divine knowledge, that there are three persons in God, and are sure also that God must, as a Divine Being, have three persons, because God cannot be other than he is. Let us help our minds to understand this by a comparison. Suppose a tower built in such a shape that it has three sides. Now, there are three distinct sides and only one tower; and whichever side we look at we see a distinct side which is not either of the other two sides, but we always can say, I see the tower. So, no matter which person of God we regard, it is always the same God.

Our holy faith teaches us that God the Father is the Divine Person who created all things, as we say in the Creed: “I believe in God, the Father Almighty, creator of heaven and earth.” It furthermore teaches us that God the Son is the Divine Person who redeemed us by becoming man and dying on the cross, as the words of the Creed declare; and again it teaches us that God the Holy Ghost is the Divine Person who sanctifies us and is the source and giver of all grace. These truths are revealed to us, and we believe them, as we do all mysteries, for the reason we give when we make an act of faith: “O my God! I believe all things taught by the holy Catholic Church, because thou, who canst neither deceive nor be deceived, hast revealed them to her.”

The Catholic Church is the voice of God to us, and when we hear her we hear God. She lives, and speaks, and acts by the Holy Ghost through Jesus Christ, our Saviour, her Divine Head. The reason some very wise people, very learned in different kinds of science, do not believe in the Trinity and other mysteries of religion as we do is because they do not hear the voice of God in the Catholic Church. It is not by science that we know the Trinity to be true, but by divine faith.

This divine faith is a gift of God, which we are bound to nourish in our souls with profound gratitude and humility, for it is a sad truth that this faith may be lost.

Catholics lose their faith by their sins, and chiefly by the sin of pride. All heretics and apostates show this in their conduct and in their words. They adhere to their own opinions and refuse to submit to the divine teaching of the church. O dear brethren! let us fear this sin of pride more than all other sin—a temptation, too, that is very apt to come up when we are ridiculed by unbelievers for our faith. Then is the time to confess the truth boldly, for if we deny our Lord before men he will deny us before the face of his Father in heaven.

Let us keep our faith by purity of life and humility of heart; for, as says the Imitation of Christ: “What doth it avail thee to discourse profoundly of the Trinity, if thou be wanting in humility, and consequently displeasing to the Trinity? If thou didst know the whole Bible by heart, and the sayings of all the philosophers, what would it profit thee without the love of God and his grace?”

Five Minute Sermons for Low Masses on All Sundays of the Year 
Volume 1
Imprimatur 1879