1 Believers have always found their satisfaction in that Divine utterance, which our ears heard recited from the Gospel at the moment when that Power, which is its attestation, was bestowed upon us:— Go now and teach all nations, baptizing them in the Name of the Father, and of the Son, and of the Holy Ghost, teaching them to observe all things whatsoever I command you; and, lo, I am with you always, even unto the end of the world. What element in the mystery of man's salvation is not included in those words?
What is forgotten, what left in darkness? All is full, as from the Divine fullness; perfect, as from the Divine perfection. The passage contains the exact words to be used, the essential acts, the sequence of processes, an insight into the Divine nature. He bade them baptize in the Name of the Father, and of the Son, and of the Holy Ghost, that is with confession of the Creator and of the Only-begotten, and of the Gift. For God the Father is One, from Whom are all things; and our Lord Jesus Christ the Only-begotten, through Whom are all things, is One; and the Spirit, God's Gift to us, Who pervades all things, is also One.
Thus all are ranged according to powers possessed and benefits conferred—the One Power from Whom all, the One Offspring through Whom all, the One Gift Who gives us perfect hope. Nothing can be found lacking in that supreme Union which embraces, in Father, Son and Holy Spirit, infinity in the Eternal, His Likeness in His express Image, our enjoyment of Him in the Gift.
Source: On the Trinity (New Advent)