Catena Aurea on Matthew 3:17: Augustine of Hippo

Here are deeds of the whole Trinity. In their own substance indeed Father, Son, and Holy Spirit are One without interval of either place or time; but in my mouth they are three separate words, and cannot be pronounced at the same time, and in written letters they fill each their several places. By this comparison may be understood how the Trinity in Itself indivisible may be manifested dividedly in the likeness of a visible creation. That the voice is that of the Father only is manifest from the words, “This is my Son.”