Under an oak - literally, "under the oak," or "the terebinth-tree." There was a single well-known tree of the kind, standing by itself in the vicinity of Bethel, which the author supposed his readers to be acquainted with.

And went after the man of God - I can hardly think that this was with any evil design. His sons had given him such an account of the prediction, the power, and influence of this prophet, that he wished to have a particular acquaintance with him, in order that he might get farther information relative to the solemn import of the prophecy which he had denounced against the idolatry at Beth-el. This good man could not have been an object of the old prophet's malevolence.

And went after the man of God, and found him sitting under an oak,.... To shelter him from the heat, and being faint, hungry, and thirsty; so the ancients of old made use of oaks for a covering, before houses were invented (e); thus Abraham pitched his tent in the plain, or under the oak, of Mamre, Genesis 13:18.

and he said unto him, art thou the man of God that camest from Judah? which he might guess at from his habit, and from the description his sons had given of him:

and he said, I am; owned himself to be the person he inquired after.

(e) Suidas in voce

And went after the man of God, and found him sitting under an oak: and he said unto him, Art thou the man of God that camest from Judah? And he said, I am.

13:11-22 The old prophet's conduct proves that he was not really a godly man. When the change took place under Jeroboam, he preferred his ease and interest to his religion. He took a very bad method to bring the good prophet back. It was all a lie. Believers are most in danger of being drawn from their duty by plausible pretences of holiness. We may wonder that the wicked prophet went unpunished, while the holy man of God was suddenly and severely punished. What shall we make of this? The judgments of God are beyond our power to fathom; and there is a judgment to come. Nothing can excuse any act of wilful disobedience. This shows what they must expect who hearken to the great deceiver. They that yield to him as a tempter, will be terrified by him as a tormentor. Those whom he now fawns upon, he will afterwards fly upon; and whom he draws into sin, he will try to drive to despair.