Albert Barnes Commentary 2 Kings 5:17

"And Naaman said, If not, yet, I pray thee, let there be given to thy servant two mules` burden of earth; for thy servant will henceforth offer neither burnt-offering nor sacrifice unto other gods, but unto Jehovah." — 2 Kings 5:17 (ASV)

Two mules’ burden of earth — Naaman thought this earth, when spread over a portion of Syrian ground, would hallow the land and make it suitable for the worship of Yahweh.