John Calvin Commentary Deuteronomy 13:18

"when thou shalt hearken to the voice of Jehovah thy God, to keep all his commandments which I command thee this day, to do that which is right in the eyes of Jehovah thy God." — Deuteronomy 13:18 (ASV)

When you shall hearken. Although this sentence depends on something else (as may be seen by referring to it), yet it is general, and extends to the commendation of the whole Law. Moses teaches first, that the rule of a holy life must be sought from the mouth of God; and then adds that He must be obeyed not partially, but universally. He also confirms what I have said respecting obedience, for people only please God when they listen to His voice. Moreover, the expression is worth our notice, in which Moses only assumes for himself the character of a minister, and claims power for God alone; for he says that he commands, but expressly explains that the commandments which he sets before them are God’s.