Albert Barnes Commentary John 15:22

"If I had not come and spoken unto them, they had not had sin: but now they have no excuse for their sin." — John 15:22 (ASV)

And spoken unto them. He declared to them the will of God and made known His requirements. Jesus had no less certainly shown by His own arguments that He was the Messiah than by His miracles. By both these kinds of proof their guilt was to be measured. See John 16:26. No small part of the Gospel of John consists of arguments used by the Savior to convince the Jews that He came from God. He here says that if He had not used these arguments and proved to them His divine mission, they would not have had sin.

Had not had sin. This is evidently to be understood of the particular sin of persecuting and rejecting Him. Of this He was speaking; and though, if He had not come, they would have been guilty of many other sins, yet of this, their great crowning sin, they would not have been guilty. We may understand this, then, as teaching:

1. That they would not have been guilty of this kind of sin. They would not have been chargeable with rejecting the signal grace of God if Jesus had not come and made an offer of mercy to them.
2. They would not have been guilty of the same degree of sin. The rejection of the Messiah was the crowning act of rebellion that brought down the vengeance of God and led to their peculiar national calamities. By way of eminence, therefore, this might be called the sin—the peculiar sin of their age and nation. (Matthew 27:25). And this shows us, what is so often taught in the Scriptures, that our guilt will be in proportion to the light that we possess and the mercies that we reject (Matthew 11:20–24; Luke 12:47–48).

If it was such a crime to reject the Savior then, it is a crime now. If the rejection of the Son of God brought such calamities on the Jewish nation, the same rejection will involve the sinner now in woe, and vengeance, and despair.

No cloak. No covering, no excuse. The proof has been so clear that they cannot plead ignorance; it has been so often presented that they cannot allege that they had no opportunity of knowing it. It is still so with all sinners.