(7) And the king said unto the man of God, Come home with me, and refresh thyself, and I will give thee a reward. (8) And the man of God said unto the king, If thou wilt give me half thine house, I will not go in with thee, neither will I eat bread nor drink water in this place: (9) For so was it charged me by the word of the LORD, saying, Eat no bread, nor drink water, nor turn again by the same way that thou camest. (10) So he went another way, and returned not by the way that he came to Bethel.
No doubt, this part of the Lord's command to the prophet was to testify his abhorrence of idols. And it became a test of his fidelity.