Hebrews 10:28

28.He that despised, etc. This is an argument from the less to the greater; for if it was a capital offense to violate the law of Moses, how much heavier punishment does the rejection of the gospel deserve, a sin which involves so many and so heinous impieties! This reasoning was indeed most fitted to impress the Jews; for so severe a punishment on apostates under the Law was neither new to them, nor could it appear unjustly rigorous. They ought then to have acknowledged that vengeance just, however severe, by which God now sanctions the majesty of his Gospel (182)

Hereby is also confirmed what I have already said, that the Apostle speaks not of particular sins, but of the entire denial of Christ; for the Law did not punish all kinds of transgressions with death, but apostasy, that is, when any one wholly renounced religion; for the Apostle referred to a passage in Deuteronomy 17:2, (183) where we find, that if any one violated God’s covenant by worshipping foreign gods, he was to be brought outside of the gate and stoned to death.

Now, though the Law proceeded from God, and Moses was not its author, but its minister, yet the Apostle calls it the law of Moses, because it had been given through him: this was said in order to amplify the more the dignity of the Gospel, which has been delivered to us by the Son of God.

Under two or three witnesses, etc. This bears not on the present subject; but it was a part of the civil law of Moses that two or three witnesses were required to prove the accused guilty. However, we hence learn what sort of crime the Apostle meant; for had not this been added, an opening would have been left for many false conjectures. But now it is beyond all dispute that he speaks of apostasy. At the same time that equity ought to be observed which almost all statesmen have adopted, that no one is to be condemned without being proved guilty by the testimony of two witnesses. (184)