“He that despised Moses' law died without mercy under two or three witnesses:”
King James Version (KJV)
10:28 He that, in capital cases, despised (presumptuously transgressed) the law of Moses died without mercy - Without any delay or mitigation of his punishment.
Heb 10:28 He that despised Moses' law. He who wilfully rebelled against the law of Moses had no remission. Died without mercy under two or three witnesses. When proved guilty by two or three witnesses his fate was death. See Nu 15:30-36 De 13:6-10. There was mercy for the ignorant, the mistaken, those "overtaken" (Ga 6:1), but not for the deliberate despiser.