Jamieson, Fausset and Brown on Leviticus 20:7-19

7-19. Sanctify yourselves therefore, and be ye holy--The minute specification of the incestuous and unnatural crimes here enumerated shows their sad prevalence amongst the idolatrous nations around, and the extreme proneness of the Israelites to follow the customs of their neighbors. It is to be understood, that, whenever mention is made that the offender was "to be put to death" without describing the mode, stoning is meant. The only instance of another form of capital punishment occurs in Le 20:14, that of being burnt with fire; and yet it is probable that even here death was first inflicted by stoning, and the body of the criminal afterwards consumed by fire (Jos 7:15).