Matthew Poole and continuators on Exodus 25:17

17 And thou shalt make a mercy-seat of pure gold two cubits and an half shall be the length thereof, and a cubit and a half the breadth thereof.

Or, Propitiatory: Which seems from the sameness of dimensions, to be nothing else but the covering of the Ark, upon which God is said to sit, whence the Ark is called Gods footstool. This covering is a manifest Type of Christ, who is therefore called the propitiation, or propitiatory, Rom. 3. 25. 1 Iohn 2. 2. and 4. 10. because he interposeth himself between God our Judge, and the Law by which we all stand condemned and accursed, Gal. 3. 10, 13. that God may not deal rigorously with us according to that Law, but mercifully for his sake who hath fulfilled the Law and therefore boldly presents himself to his Father on our behalf.