Deuteronomy 6:13 - Joseph Benson’s Commentary on the Old and New Testaments

Shall swear by his name Not by idols, or any creatures, but only by his name, when thou hast a call and just cause to swear. But some think, from comparing this with other passages, the words rather mean, that they were to be steadfast in the acknowledgment and worship of the true God, and in professing that religion which he had instituted. Thus, (Isaiah 19:18,) to swear to the Lord of hosts, is to profess the true religion. And God's words, by the same prophet, (Isaiah 45:23,) Unto me every knee shall bow, and every tongue shall swear, are interpreted by St. Paul to mean, Every tongue shall confess to God, Romans 14:11. Thus, (Psalms 63:11,) Every one that sweareth by him, signifies, every worshipper of the true God.