Jamieson, Fausset and Brown on Deuteronomy 17:2-7

De 17:2-7. Idolaters Must Be Slain.

2-7. If there be found among you ... man or woman, that hath wrought wickedness--The grand object contemplated in choosing Israel was to preserve the knowledge and worship of the one true God; and hence idolatry of any kind, whether of the heavenly bodies or in some grosser form, is called "a transgression of His covenant." No rank or sex could palliate this crime. Every reported case, even a flying rumor of the perpetration of so heinous an offense, was to be judicially examined; and if proved by the testimony of competent witnesses, the offender was to be taken without the gates and stoned to death, the witnesses casting the first stone at him. The object of this special arrangement was partly to deter the witnesses from making a rash accusation by the prominent part they had to act as executioners, and partly to give a public assurance that the crime had met its due punishment.