Jamieson, Fausset and Brown on 2 Kings 5:17

17. two mules' burden of earth--with which to make an altar (Ex 20:24) to the God of Israel. What his motive or his purpose was in this proposal--whether he thought that God could be acceptably worshipped only on his own soil; or whether he wished, when far away from the Jordan, to have the earth of Palestine to rub himself with, which the Orientals use as a substitute for water; or whether, by making such a request of Elisha, he thought the prophet's grant of it would impart some virtue; or whether, like the modern Jews and Mohammedans, he resolved to have a portion of this holy earth for his nightly pillow--it is not easy to say. It is not strange to find such notions in so newly a converted heathen.