John Gill 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 listen to the voice of the Lord your God
Not only in this case, but in all others:

to keep all his commandments which I command you this day :
the repetition of which he made to them, and enjoined the observance of them in the name of the Lord:

to do that which is right in the eyes of the Lord your God ;
which they would do, if they kept the commandments of the Lord, which are holy, just, and good, and must be right in his sight because commanded by him.