What does Hebrews 10:28 mean?

In the Old Testament, God made certain provisions for sin. However, these temporary means of atonement assumed that the person who sinned did so in a moment of passion, or ignorance, or simple error. The reference here to those who "set aside the law of Moses" means those who willingly, purposefully, spitefully rejected God's laws (Numbers 15:27–31). In those cases, the old covenant made no provision for atonement. In simple terms, the Law of Moses treated intentional defiance of God as an unforgivable sin.

That level of sin, under the old covenant, carried the death penalty. As such, the Law of Moses required several independent witnesses in order for the charge to be valid. This letter to Jewish Christians has, to this point, placed great emphasis on how the new covenant is greater to the old covenant. In the next verses, the writer will extend this idea to the consequences of rejection. If rejecting the old covenant meant death, how severe are the consequences for those who reject the new covenant?