‘As Moses the servant of YHWH had commanded the children of Israel, as it is written in the book of the law of Moses, an altar of hewn stones on which no man had lifted up any iron.'
Joshua was carefully carrying out the instructions that he had received from Moses. The altar of unhewn stones was as instructed in Exodus 20:25. The forbidding here of iron probably represents iron as a foreign and ‘new' metal, not native to Israel. But in fact all tools were forbidden.
‘And they offered on it burnt offerings to YHWH, and sacrificed peace offerings.'
Having built the altar, worship was now offered, both in the form of dedicatory, atoning whole burnt offerings (Leviticus 1), and in atoning sacrifices in a form in which the people could participate by eating of the peace offerings (Leviticus 3; Leviticus 7:11-18). This was both in thanksgiving for victory and in preparation for renewal of the covenant, and acceptance into it of the people of Shechem (Deuteronomy 27:6-7).