Deuteronomy 10:20
Thou shalt fear the LORD thy God; him shalt thou serve, and to him shalt thou cleave, and swear by his name.
Thou shalt fear the Lord thy God,.... Which includes the whole worship of him, external and internal:
him shalt thou serve; heartily and sincerely, according to his revealed will, and him only:
and to him shall thou cleave; and not turn aside to follow other gods, and worship them:
and swear by his name; and his only, whenever it is necessary to take an oath, which should not be done rashly or on trivial accounts; and never by any creature, but by the living God; see Deuteronomy 6:13.