This covenant was not the one God made with the Israelites at Sinai. It was the one he first made with Abraham, then with Isaac and Jacob (Genesis 15:1–21; 17:1–21; Genesis 26:1–5; Genesis 28:1–4, 13–15; 46:1–4).
For a covenant to be legal and proper, all parties had to swear an oath. Although God, by his nature, could never break a promise, he followed this custom (see Deuteronomy 7:12).