The saint meets those who in Jewish wise object to the order of the words: “In the name of the Father and of the Son and of the Holy Ghost,” with the retort that the Son also is often placed before the Father; though he first points out that an answer to this objection has been already given by him.
115. Why is it that the Arians, after the Jewish fashion, are such false and shameless interpreters of the divine words, going indeed so far as to say that there is one power of the Father, another of the Son, and another of the Holy Ghost, since it is written: “Go, teach all nations, baptizing them in the name of the Father and of the Son and of the Holy Ghost”? And why do they make a distinction of divine power owing to the mere order of words?
116. Though I have already given this very witness for a unity of majesty and name in my former books, yet if they make this the ground of debate, I can maintain on the testimony of the Scriptures that the Son is mentioned first in many places, and that the Father is spoken of after Him. Is it therefore a fact that, because the name of the Son is placed first, by the mere accident of a word, as the Arians would have it, the Father comes second to the Son? God forbid, I say, God forbid. Faith knows nothing of such order as this; it knows nothing of a divided honour of the Father and the Son. I have not read of, nor heard of, nor found any varying degree in God. Never have I read of a second, never of a third God. I have read of a first God, I have heard of a first and only God.
117. If we pay such excessive regard to order, then the Son ought not to sit at the right hand of the Father, nor ought He to call Himself the First and the Beginning. The Evangelist was wrong in beginning with the Word and not with God, where he says: “In the beginning was the Word, and the Word was with God.” For, according to the order of human usage, he ought to name the Father first. The Apostle also was ignorant of their order, who says: “Paul the servant of Jesus Christ, called to be an Apostle, separated unto the Gospel of God;” and elsewhere: “The grace of our Lord Jesus Christ, and the love of God, and the communion of the Holy Ghost.” If we follow the order of the words, he has placed the Son first, and the Father second. But the order of the words is often changed; and therefore you ought not to question about order or degree, in the case of God the Father and His Son, for there is no severance of unity in the Godhead.
Source: On the Christian Faith (De fide) (New Advent)