New Defender's Study Bible Notes
5:17 unto other gods. Naaman was a worthy man, so that his military victories had been given by the Lord (II Kings 5:1), possibly already at least partially trusting the God of Israel as a result of the testimony of the captive maid (II Kings 5:4). After his miraculous healing he became a true believer, though still forced to give nominal allegiance to the gods of Syria (II Kings 5:18).
5:17 two mules’ burden of earth. Naaman apparently believed that, if he was going to worship the God of Israel henceforth, he would need to have some of the ground of Israel on which to do so.