Both of these phrases "the covenant" and "the oath" refer to the same promise that Yahweh made to his people. (See: [[rc://en/ta/man/jit/figs-parallelism]])
The words "that he made" are undestood from the previous phrase. They can be repeated. Alternate translation: "his oath that he made to Isaac" or "his oath that he gave to Isaac" (See: [[rc://en/ta/man/jit/figs-explicit]])