4 Let us attend to the Gospel; just now the Lord was speaking, and let us do what He said. “He that believes in Me,” says He, “passes from death unto life, and comes not into judgment. Verily I say unto you, that the hour shall come, and now is, when the dead shall hear the Voice of the Son of God, and they that hear shall live. For as the Father has life in Himself, so has He given to the Son to have life in Himself.” By begetting Him He gave it; in that He begot, He gave it.
For the Son is of the Father, not the Father of the Son; but the Father is the Father of the Son, and the Son is the Son of the Father. I say the Son is begotten of the Father, not the Father of the Son; and the Son was always, always therefore begotten. Who can comprehend this “always begotten”? For when any man hears of one begotten, it occurs to him; “Therefore there was a time, when he who was begotten was not.” What say we then? Not so; there was no time before the Son, for that “all things were made by Him.” If all things were made by Him, times also were made by Him; how could times be before the Son, by whom times were made?
Take away then all times, the Son was with the Father always. If the Son were with the Father always, and yet the Son, He was begotten always; if begotten always, He who was begotten was always with Him That begot Him.
Source: Sermons on Selected Lessons of the New Testament (New Advent)