Charles Ellicott Commentary 2 Kings 3:8

"And he said, Which way shall we go up? And he answered, The way of the wilderness of Edom." — 2 Kings 3:8 (ASV)

And he said — that is, Jehoram said.

Which way. — They might cross the Jordan and attack the northern frontier of Moab, or they might round the southern end of the Dead Sea and invade Moab from the side of Edom. The former was the shortest route for both kings.

But Moab’s strongest defences were on the north frontier, and the allies would be liable to attacks from the Syrians in Ramoth-gilead (2 Kings 8:28). The longer and more difficult southern road may have been chosen partly for these reasons.

It may also have been chosen because Jehoshaphat wished to march as far as possible within his own territory, to get a contingent from Edom (which was at this time subject to him, 1 Kings 22:48), and perhaps to hold it in check. Moreover, the Moabites were less likely to be on their guard on the southern border, which was more difficult to access.

And he answered. — Said — that is, Jehoshaphat.