Saint Augustine on the Most Holy Trinity [As Seen by the Angels in Heaven]

Those holy angels come to the knowledge of God not by audible words, but by the presence to their souls of immutable truth, i.e., of the only-begotten Word of God; and they know this Word Himself, and the Father, and their Holy Spirit, and that this Trinity is indivisible, and that the three persons of it are one substance, and that there are not three Gods but one God; and this they so know that it is better understood by them than we are by ourselves.

— St. Augustine of Hippo, The City of God, Book 2 Chapter 29.

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Holy Spirit Prayer of St. Augustine

Breathe into me, Holy Spirit, that my thoughts may all be holy. Move in me, Holy Spirit, that my work, too, may be holy. Attract my heart, Holy Spirit, that I may love only what is holy. Strengthen me, Holy Spirit, that I may defend all that is holy. Protect me, Holy Spirit, that I may always be holy. Amen.