“the book of the law of Moses.” The revelation that God gave to Moses had already been collected and was being used for guidance as to how to obey God and live life (cp. Exod. 24:4; Deut. 31:9). Many people assert that the laws and records of ancient Israel were passed down from generation to generation as part of an oral tradition before they were written down, but that is just an assumption, there is no proof that occurred. The Bible records that things were written down pretty much as they occurred, and then, like here in Joshua, people checked the writings and obeyed them.
“an altar of uncut stones.” This was commanded in Deuteronomy 27:4-6. The phrase “uncut stones” is “complete stones,” whole stones, in the Hebrew text, that is stones that have not been cut down and formed. The altar was not to be a thing of beauty, but a place of atonement for sin, and sin and death are not pretty or to be admired. The word “altar” in Hebrew means “slaughter site” or “sacrificing place.” It was a place of death, but death that pointed to atonement.