There was not a word of all that Moses commanded, which Joshua didn't read before all the assembly of Israel, and the women, and the little ones, and the foreigners who were among them.
It is important for God’s people to declare their allegiance to His revealed will publicly among the unbelievers with whom we live (cf. Acts 1:8). This helps them understand why we live as we do, and it brings glory to God when His people then proceed to live upright lives and demonstrate His supernatural power (cf. Matthew 5:16).