11 In order to seeing this more plainly, consider that which the same Lord also says of the Jews, “If I had not come and spoken to them, they had not had sin.” For this again was not said with any such meaning, as if He intended it to be understood that the Jews would have been without any sin at all, if He had not come and spoken to them. For indeed He found them full of and laden with sins. Wherefore He says, “Come unto Me, all you that labour and are heavy laden.” Laden!
With what, but with the burdens of sins and transgressions of the Law? “For the Law entered that sin might abound.” Since then He says Himself in another place, “I came not to call the righteous, but sinners to repentance;” how would “they not have had sin if He had not come”? If it be not that this proposition being expressed neither universally, nor particularly, but indefinitely, does not constrain us to understand it of all sin? But certainly unless we understand that there was some sin which they would not have had if Christ had not come and spoken unto them, we must say that the proposition was false, which God forbid.
He does not say then, “If I had not come and spoken unto them, they had had no sin;” lest the Truth should lie. Nor again did He say definitely, “If I had not come and spoken unto them, they had not had some certain sin;” lest our devout earnestness should not be exercised. For in the full abundance of the Holy Scriptures we feed upon the plain parts, we are exercised by the obscure: by the one, hunger is driven away, and daintiness by the other. Seeing then that it is not said, “they had had no sin,” we need not be disturbed, though we acknowledge that the Jews would have been sinners, even if the Lord had not come.
But yet because it is said, “If I had not come, they had not had sin;” it must needs be that they contracted, though not all, yet some sin which they had not before, from the coming of the Lord. And this verily is that sin, that they believed not in Him who was present with and spoke to them, and that counting Him as an enemy because He spoke the truth, they put Him besides to death. This sin so great and terrible it is clear they had not had if He had not come and spoken to them.
As then when we hear the words, “They had not had sin;” we do not understand all, but some, sin; so when we hear in today's lesson, “Blasphemy of the Spirit shall not be forgiven;” we understand not all, but a certain kind of blasphemy; and when we hear, “Whosoever speaks a word against the Holy Ghost, it shall not be forgiven him;” we ought not to understand every, but some certain word.
Source: Sermons on Selected Lessons of the New Testament (New Advent)