4 To His creatures has He given to beget that which they are. To His creatures, to mortal, earthly creatures, has God given, has granted to beget that which they are; and do you think that He has not been able to reserve this for Himself, He who is before all ages? Should He who has no beginning of time, beget a son, different from That which Himself is, beget a degenerate son? Hear how great a blasphemy it is to say, that the Only Son of God is of another substance.
Most certainly if He is so, He is degenerate. If you should say to any child of man, “You are degenerate,” how great an offense is it! And yet in what sense is any child of man said to be degenerate? As, for example, his father is brave, he is a poltroon and a coward. If any one sees him, and would rebuke him, as he thinks of his brave father, what does he say to him? “Get you hence, you degenerate one!” What is “degenerate one”? “Your father was a brave man, and you tremble through fear.”
He to whom this is said, is degenerate by some fault, by nature he is equal. What is, “by nature he is equal”? He is a man, which his father also is. But the one brave, the other a coward; the one bold, the other timid; yet both men. By some fault then he is degenerate, not by nature. But when you say, that the Only Son, the One Son of the Father, is degenerate, you say nought else, but that He is not What the Father is; and you do not say, that having been already born, He has become degenerate; but He was begotten so. Who can endure this blasphemy? If they could in any sort whatever see this blasphemy, they would fly from it, and become Catholics.
Source: Sermons on Selected Lessons of the New Testament (New Advent)