60 Grk “they would not have sin” (an idiom). Jesus now describes the guilt of the world. He came to these people with both words (15:22) and sign-miracles (15:24), yet they remained obstinate in their unbelief, and this sin of unbelief was without excuse. Jesus was not saying that if he had not come and spoken to these people they would be sinless; rather he was saying that if he had not come and spoken to them, they would not be guilty of the sin of rejecting him and the Father he came to reveal. Rejecting Jesus is the one ultimate sin for which there can be no forgiveness, because the one who has committed this sin has at the same time rejected the only cure that exists. Jesus spoke similarly to the Pharisees in 9:41: “If you were blind, you would have no sin (same phrase as here), but now you say ‘We see’ your sin remains.”

In other versions

If I had not come and spoken to them, they would not have been guilty of sin, but now they have no excuse for their sin.

If I had not come and spoken to them, they would not be guilty of sin; but now they have no excuse for their sin.

If I had not come and spoken to them, they would not be guilty of sin. Now they have no excuse for their sin.

They would not be guilty if I had not come and spoken to them. But now they have no excuse for their sin.

If I had not come and spoken to them, they would not have sin. But now they do not have a valid excuse for their sin.

If I had not come and spoken unto them, they had not had sin: but now they have no cloke for their sin.

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