How do we know God's judgment is justified?

The judgment of God, as seen in Achan's case, is grounded in His absolute holiness. God is inherently righteous and cannot overlook sin, whether it is an individual act like Achan's or collective sin within Israel. This aligns with the Biblical principle that 'the soul that sins shall die' (Ezekiel 18:4). The swift justice rendered against Achan serves to illustrate the truth that sin must be addressed, and when left unaccounted for, it disrupts the covenant community. God's justice, therefore, is both necessary and warranted, ensuring His holiness is upheld.