Matthew Henry Commentary Joshua 8:30-35

"Then Joshua built an altar unto Jehovah, the God of Israel, in mount Ebal, as Moses the servant of Jehovah commanded the children of Israel, as it is written in the book of the law of Moses, an altar of unhewn stones, upon which no man had lifted up any iron: and they offered thereon burnt-offerings unto Jehovah, and sacrificed peace-offerings. And he wrote there upon the stones a copy of the law of Moses, which he wrote, in the presence of the children of Israel. And all Israel, and their elders and officers, and their judges, stood on this side of the ark and on that side before the priests the Levites, that bare the ark of the covenant of Jehovah, as well the sojourner as the homeborn; half of them in front of mount Gerizim, and half of them in front of mount Ebal; as Moses the servant of Jehovah had commanded at the first, that they should bless the people of Israel. And afterward he read all the words of the law, the blessing and the curse, according to all that is written in the book of the law. There was not a word of all that Moses commanded, which Joshua read not before all the assembly of Israel, and the women, and the little ones, and the sojourners that were among them." — Joshua 8:30-35 (ASV)

As soon as Joshua reached the mountains Ebal and Gerizim, without delay and regardless of the unsettled state of Israel or their enemies, he confirmed the Lord's covenant with His people, as commanded (Deuteronomy 11 and Deuteronomy 27). We must not think to postpone covenanting with God until we are settled in the world, nor must any business keep us from focusing on and pursuing the one thing needful. The way to prosper is to begin with God (Matthew 6:33).

They built an altar and offered sacrifice to God as a sign of their dedicating themselves to God, as living sacrifices to His honor, through a Mediator. By Christ's sacrifice of Himself for us, we have peace with God.

It is a great mercy to any people to have the law of God in writing, and it is fitting that the written law should be in a language they understand, so that it may be seen and read by everyone.