Our God, we believe in Thee, the Father and the Son and the Holy Spirit
"O Lord our God, we believe in Thee, the Father and the Son and the Holy Spirit. For the Truth would not say, Go, baptize all nations in the name of the Father and of the Son and of the Holy Spirit, unless Thou wast a Trinity. Nor wouldest thou, O Lord God, bid us to be baptized in the name of Him who is not the Lord God. Nor would the divine voice have said, Hear, O Israel, the Lord thy God is one God, unless Thou wert so a Trinity as to be one Lord God. And if Thou, O God, weft Thyself the Father, and weft Thyself the Son, Thy Word Jesus Christ, and the Holy Spirit your gift, we should not read in the book of truth, "God sent His Son;" nor wouldest Thou, O Only-begotten, say of the Holy Spirit, "Whom the Father will send in my name;" and, "Whom I will send to you from the Father." Directing my purpose by this rule of faith, so far as I have been able, so far as Thou hast made me to be able, I have sought Thee, and have desired to see with my understanding what I believed; and I have argued and labored much. O Lord my God, my one hope, hearken to me, lest through weariness I be unwilling to seek Thee, "but that I may always ardently seek Thy face." Do Thou give strength to seek,, who hast made me find Thee, and hast given the hope of finding Thee more and more. My strength and my infirmity are in Thy sight: preserve the one, and heal the other.
My knowledge and my ignorance are in Thy sight; where Thou hast opened to me, receive me as I enter; where Thou hast closed, open to me as I knock. May I remember Thee, understand Thee, love Thee. Increase these things in me, until Thou renewest me wholly. I know it is written, "In the multitude of speech, thou shalt not escape sin." But O that I might speak only in preaching Thy word, and in praising Thee! Not only should I so flee from sin, but I should earn good desert, however much I so spake. For a man blessed of Thee would not enjoin a sin upon his own true son in the faith, to whom he wrote, "Preach the word: be instant in season. out of season." Are we to say that he has not spoken much, who was not silent about Thy word, O Lord, not only in season, but out/of season? But therefore it was not much, because it was only what was necessary. Set me free, O God, from that multitude of speech which I suffer inwardly in my soul, wretched as it is in Thy sight, and flying for refuge to Thy mercy; for I am not silent in thoughts, even when silent in words. And if, indeed, I thought of nothing save what pleased Thee, certainly I would not ask Thee to set me free from such multitude of speech. But many are my thoughts, such as Thou knowest, "thoughts of man, since they are vain." Grant to me not to consent to them; and if ever they delight me, nevertheless to condemn them, and not to dwell in them, as though I slumbered. Nor let them so prevail in me, as that anything in my acts should proceed from them; but at least let my opinions, let my conscience, be safe from them, under Thy protection. When the wise man spake of Thee in his book, which is now called b the special name of Ecclesiasticus, We speak," he said, "much, and yet co e short; and in sum of words, He is all." When, therefore, we shall have come to Thee, these very many things that we speak, and yet come short, will cease; and Thou, as One, wilt remain "all in all." And we shall say one thing without end, in praising Thee in One, ourselves also made one in Thee. O Lord the one God, God the Trinity, whatever I have said in these books that is of Thine, may they acknowledge who are Thine; if anything of my own, may it be pardoned both by Thee and by those who are Thine. Amen."
St Augustine, On the Trinity, 15,51