Charles Ellicott Commentary Deuteronomy 6:13

"Thou shalt fear Jehovah thy God; and him shalt thou serve, and shalt swear by his name." — Deuteronomy 6:13 (ASV)

Thou shalt fear the Lord thy God, and serve him. —Literally, Jehovah your God you shall fear, and Him you shall serve: that is, Him only, as translated by the Septuagint, and cited by our Lord in His temptation. It is remarkable that all His answers to the tempter were taken not only from Deuteronomy, but from one and the same portion of Deuteronomy—Deuteronomy 5-10 inclusive—the portion which applies the principles of the Decalogue to Israel’s life.

And shalt swear by his name. —Compare Exodus 23:13: Make no mention of the name of other gods. The principle was not unknown to the patriarchs. Laban appealed to the God of Nahor, but Jacob sware by the fear of his father Isaac (Genesis 31:53). (Compare Jeremiah 5:7: Thy children have forsaken me, and sworn by ... no-gods.)