Hebrews 10:28

He that despised Moses' law - Αθετησας· He that rejected it, threw it aside, and denied its Divine authority by presumptuous sinning, died without mercy - without any extenuation or mitigation of punishment; Numbers 15:30.

Under two or three witnesses - That is, when convicted by the testimony of two or three respectable witnesses. See Deuteronomy 17:6.

He that despised Moses' law - That is, the apostate from the religion of Moses. It does not mean that in all cases the offender against the Law of Moses died without mercy, but only where offences were punishable with death, and probably the apostle had in his eye particularly the case of apostasy from the Jewish religion. The subject of apostasy from the Christian religion is particularly under discussion here, and it was natural to illustrate this by a reference to a similar case under the Law of Moses. The Law in regard to apostates from the Jewish religion was positive. There was no reprieve; Deuteronomy 13:6-10.

Died without mercy - That is, there was no provision for pardon.

Under two or three witnesses - It was the settled law among the Hebrews that in all cases involving capital punishment, two or three witnesses should be necessary. That is, no one was to be executed unless two persons certainly bore testimony, and it was regarded as important, if possible, that three witnesses should concur in the statement. The object was the security of the accused person if innocent. The "principle" in the Law was, that it was to be presumed that two or three persons would be much less likely to conspire to render a false testimony than one would be, and that two or three would not be likely to be deceived in regard to a fact which they had observed.

10:28 He that, in capital cases, despised (presumptuously transgressed) the law of Moses diedwithout mercy - Without any delay or mitigation of his punishment.