Joshua 8:31
As Moses the servant of the LORD commanded the children of Israel, as it is written in the book of the law of Moses, an altar of whole stones, over which no man hath lift up any iron: and they offered thereon burnt offerings unto the LORD, and sacrificed peace offerings.
The altar was erected after Achan had been punished and the second advance against Ai had ended in victory. It belonged to a solemn religious gathering at Shechem held before Israel took possession of its inheritance, with men, women, children and resident strangers present. Because obedience to God was Israel's only hope, Joshua assembled all the people as Moses had commanded.
On Mount Ebal he built the altar of whole, unhewn stones over which no iron tool had been lifted, exactly as Moses had commanded, and offered burnt offerings and peace offerings to the Lord upon it. At that gathering he rehearsed the blessings that would follow obedience to the law and the curses that would fall if it were disregarded, repeating the Ten Commandments and also all the statutes and precepts which Moses had recorded. By this public recognition of the law the people renewed their covenant loyalty to God.
The altar stood on the mountain where the curse was pronounced, showing that Israel's transgression of God's law justly brings divine wrath. The altar and its sacrifices represented the atonement of Christ, through which that judgment would be withheld. Afterward Ebal and Gerizim stood as witnesses to the solemn vows the people renewed at Shechem before Joshua.