Jamieson, Fausset and Brown on 1 Kings 18:46

46. Elijah ... girded up his loins, and ran before Ahab--It was anciently, and still is in some countries of the East, customary for kings and nobles to have runners before their chariots, who are tightly girt for the purpose. The prophet, like the Bedouins of his native Gilead, had been trained to run; and, as the Lord was with him, he continued with unabated agility and strength. It was, in the circumstances, a most proper service for Elijah to render. It tended to strengthen the favorable impression made on the heart of Ahab and furnished an answer to the cavils of Jezebel for it showed that he who was so zealous in the service of God, was, at the same time, devotedly loyal to his king. The result of this solemn and decisive contest was a heavy blow and great discouragement to the cause of idolatry. But subsequent events seem to prove that the impressions, though deep, were but partial and temporary.