Jamieson, Fausset and Brown on Exodus 25:17

17. thou shalt make a mercy seat of pure gold--to serve as a lid, covering it exactly. It was "the propitiatory cover," as the term may be rendered, denoting that Christ, our great propitiation [1Jo 2:2; 4:10], has fully answered all the demands of the law, covers our transgressions, and comes between us and the curse of a violated law.