Charles Ellicott Commentary Deuteronomy 10:20

"Thou shalt fear Jehovah thy God; him shalt thou serve; and to him shalt thou cleave, and by his name shalt thou swear." — Deuteronomy 10:20 (ASV)

Thou shalt fear the Lord thy God; him shalt thou serve. —In the New Testament, “Thou shalt worship the Lord thy God, and him only shalt thou serve.” It was our Lord’s last answer to the tempter in the wilderness. The order of the Hebrew gives the emphasis. “Jehovah thy God shalt thou fear, Him shalt thou serve, and to Him shalt thou cleave;” “and (adds Rashi) after all these qualities are established in you, then you shall swear by His name.” At least His name would not be profaned in such a case.