The tribes present a powerful declaration of their absolute innocence, offering a conditional oath to clear their names. They express a complete willingness to accept severe divine punishment if their motives for building their new altar were corrupt. They clarify that if their true intention was to abandon the path of God, they fully deserve to be punished [מצודת דוד, ביאור שטיינזלץ]. This addresses the first major accusation against them, which is the severe sin of idolatry.
Their defense also carefully addresses a second potential offense. Beyond the threat of idolatry, they deny any plan to actually use the altar for burnt offerings and grain offerings. This specific detail responds to the suspicion of rebellion. The fear was that they were attempting to break away from the central Tabernacle in Shiloh to establish an independent site for sacrifices [מלבי״ם].
To counter both the accusation of idolatry and the accusation of rebellion, the tribes conclude their defense by placing their fate entirely in divine hands. The primary approach among commentators is that this final plea represents a total acceptance of God's justice. The tribes declare that if they are secretly guilty of either offense, God Himself will uncover their true intentions, hold them accountable, and deliver the exact punishment they deserve.