Charles Ellicott Commentary 1 Kings 20:23

"And the servants of the king of Syria said unto him, Their god is a god of the hills; therefore they were stronger than we: but let us fight against them in the plain, and surely we shall be stronger than they." — 1 Kings 20:23 (ASV)

Gods of the hills. —The idea of tutelary gods, whose strength was greatest on their own soil, is naturally common in polytheistic religions, which, by the very multiplication of gods, imply a limitation of the power of each. Now, the greater part of the territory where Jehovah was worshipped was a hill-country. Samaria in particular, the scene of recent defeat, lay in the mountain region of Ephraim. Moreover, the Israelite armies, being mostly infantry—having, indeed, few or no cavalry, except in the time of Solomon—naturally encamped and fought, as far as possible, on the hills, as Barak did on Mount Tabor (Judges 4:6–14), Saul on Mount Gilboa (1 Samuel 31:1), and Ahab himself (1 Kings 20:27).

Perhaps the worship of Jehovah in the “high places” may have also contributed to this belief that the “gods of Israel were gods of the hills,” whose power vanished in the plains.

In the plains, of course, the Syrian armies of chariots and horsemen would naturally fight at an advantage.

Shrewd policy might, as is often the case, have lurked in the advice of Ben-hadad’s counselors under the cover of superstition.

Indeed, this policy also seems to manifest in their seizing the opportunity to increase central power by organizing the troops of the tributary kings under his own officers.