What does Hebrews 10:18 mean?

This verse completes the writer's long explanation of the superiority of the new covenant. Earlier, the writer had made a powerful point about the animal sacrifices of the old covenant. Since they were offered over and over, it was clear they could not actually take away sin (Hebrews 9:8–10). If they could, the priests would have stopped offering them (Hebrews 10:1–2). Instead, they continued to bring animal blood, in obedience, and as a reminder of sin (Hebrews 10:3–4).

Sacrifice was described as absolutely necessary for the forgiveness of sins (Hebrews 9:22). However, animal blood could not accomplish the salvation of man. It could settle ceremonial issues, but not change the sinful inner being. Christ's sacrifice, on the other hand, was entirely human, and entirely perfect. This is why Jesus is described as "seated" in heaven, symbolizing His finished work (Hebrews 10:12).

As the writer points out here, when sin is truly forgiven, there "is no longer any offering." This means that once a truly saving sacrifice has been offered, there is no reason to offer any further sacrifices for sin. An additional meaning to this statement, given later, is a warning. Those who turn away from Jesus are abandoning the one and only remedy for their sin.