John 8:21, “I am going away, and you will seek Me, and you will die in your sin. Where I am going, you cannot come.”
Whom is Jesus speaking to here? Unbelieving Pharisees. When Jesus said this to them, they thought it meant Jesus was going to kill Himself (v. 22). But He made a distinction between Him and them—they are of this corrupt world, and Jesus is not. Then He repeats Himself, “I told you that you would die in your sins, for unless you believe that I am He, you will die in your sins” (v. 24). Who is He? The Son of Man (v. 28).
This can either be Law or Gospel, depending on who the hearer is. If the hearer is an unbeliever, it is Law, for he hears condemnation—when he dies, he dies in sin, and he dies condemned. If the hearer is a believer, it is Gospel, for she hears salvation—when she dies, she dies blameless, and she dies justified. Therefore, brothers and sisters, know this: Though we still suffer sin in this world, we will not die in sin, for the Son of Man was lifted up to bear our transgressions.
The Lutheran Column 