John 15:22

“If I had not come and spoken to them, they had not had sin. But now they have no excuse for their sin.”

This is the crux of the matter. Jesus has come as a light into the world (John 3:16; John 8:12). His words have shone like a searchlight piercing into men's innermost being (compare John 7:7). But men shy from the light, for it reveals what they are. They love darkness rather than light because by coming to the light what they do is shown to be evil in God's eyes (John 3:19). Previously such men had been living in a self-satisfied state, not fully aware of the inadequacy of what they believed. They were not aware of how sinful they were. But by His words Jesus has brought home to them that inadequacy, undermining much of what they cherished, especially their sense of their own spiritual achievements. Thus they no longer have any excuse, and if they are unwilling to admit it, and change, they will hate Him for what He has done. It is always difficult to admit that we have been wrong and to begin again.