John 15:22

If I had not come and spoken unto them
The ignorance of the Jews is represented as inexcusable, since Christ was come, and had preached unto them; if he had not come and told them that he was the Messiah, they might have pleaded an excuse for their ignorance of him, and his mission, and of the Father that sent him: but inasmuch as he was come in the flesh, and came to them his own; and came also a light into the world, carrying along with him evidence, conviction, and demonstration, of his being the Messiah; speaking such words as never man did; preaching with such authority as the Scribes and Pharisees did not; declaring in plain terms he was the Christ of God, and that if they did not believe him to be so, they would die in their sins; they could have no pretext to make for their ignorance and disbelief: if all this had not been done,

they had not had sin;
or been guilty of the sin of unbelief, in the rejection of the Messiah; not that they would have been without sin in any sense, or without any kind of sin, but without this particular sin; at least they would have excused and wiped themselves clean, and would have looked like innocent and sinless persons, under all their ignorance and unbelief:

but now they have no cloak for their sin;
they could not say, had he come to us, and told us that he was the Messiah, and given evidence of his being sent by the Father, we would have believed him, and received him as the Messiah; for he did do this, and so cut off all excuses and pretences from them.