Moses wrote, to wit, in a book, Hebrews 9:19. And the ten commandments God himself wrote also in tables of stone, Exodus 31:18. Builded an altar; representing God in Christ, as one party in the covenant. Twelve pillars; representing the people of Israel, the other party. So here are the outward signs and symbols of a covenant made between God and the Israelites.
Related Commentaries of Exodus 24:4
Exodus 24:4
4 And Moses wrote all the words of the LORD, and rose up early in the morning, and builded an altar under the hill, and twelve pillars, according to the twelve tribes of Israel.