in regard to sin, because men do not believe in me;
The Spirit is going to convince or convict the world of sin, not just tell them about it. He will actually prove to them that they are sinners and bring them to the point of admitting this truth, much like Jesus did in (8:9). (Or was it the Spirit there who convicted them?) Primarily, the sin the Spirit will be convicting the world of is the sin of unbelief. This is the sin that condemns the world to eternal punishment. Unbelief is the most basic of all sins. The definition of sin is to live for my self and to make my self the master and center of my world and that is exactly what unbelief does. It does not recognize the need for Jesus or His atoning death and it does not recognize the need to let Christ rule one’s life. All other sins are a matter of giving into temptations or the sinful nature, but unbelief is the sin out of which those other sins flow, because if I am the king of my universe then I can do anything and everything I want. (John 3:19)
John 8:9 At this, those who heard began to go away one at a time, the older ones first, until only Jesus was left, with the woman still standing there.
John 3:19 This is the verdict: Light has come into the world, but men loved darkness instead of light because their deeds were evil.