Albert Barnes Commentary 1 Kings 13:9

"for so was it charged me by the word of Jehovah, saying, Thou shalt eat no bread, nor drink water, neither return by the way that thou camest." — 1 Kings 13:9 (ASV)

Eat no bread, nor drink water — The reason for this command is evident. The man of God was not to accept hospitality from anyone in Bethel, in order to demonstrate in a tangible way—one that people could readily understand—God’s abhorrence of the system Jeroboam had devised of his own heart.

Nor turn again by the same way that you came — This command seems to have been given simply to test the prophet’s obedience by placing him under a positive command as well as a moral obligation.