3 “He Who sent Me,” says He, you have heard it; “He Who sent Me,” says He, “He gave Me a commandment what I should say, and what I should speak; and I know that His commandment is life everlasting.” It is John's Gospel, hold it fast. “He Who sent Me, He gave Me a commandment what I should say, and what I should speak; and I know that His commandment is life everlasting.” O that He would grant me to say what I wish! For my poverty and His abundance straitens me. “He,” says He, “gave Me a commandment, what I should say, and what I should speak; and I know that His commandment is life everlasting.” Search in the Epistle of this John the Evangelist for what he has said of Christ.
“Let us believe,” he says, “His True Son Jesus Christ. This is the True God and Everlasting Life.” What is, “The True God, and Everlasting Life”? The True Son of God is the “the True God, and Everlasting Life.” Why did He say, “On His True Son”? Because God has many sons, therefore was He to be distinguished, by adding that He was the True Son. Not by simply saying that He is the Son; but by adding, as I have said, that He is the True Son; therefore He was to be distinguished, because of the many sons which God has. For we are sons by grace, He by Nature. We made by the Father through Him; He Himself That Which the Father is; are we too That Which God is?
Source: Sermons on Selected Lessons of the New Testament (New Advent)