Albert Barnes Commentary Isaiah 16:12

"And it shall come to pass, when Moab presenteth himself, when he wearieth himself upon the high place, and shall come to his sanctuary to pray, that he shall not prevail." — Isaiah 16:12 (ASV)

When it is seen - When it occurs; that is, when Moab actually “becomes” weary.

Is weary on the high place - The “high place” denotes the place of idolatrous worship, and in this context, means the same as the temple of Chemosh or his sanctuary. Temples and altars were usually constructed on such high places, especially the temples of pagan gods. Moab is represented here as looking to her gods for protection. Weary, exhausted, and worn down by calamities, she is depicted as fleeing from the desolate towns and cities, taking refuge at the altar, and seeking assistance there.

This, says Jerome, is the final misery. She is now forsaken by those aids in which she had always trusted and on which she had relied. Her people slain, her towns destroyed, her strong places broken down, and her once fertile fields languishing and desolate, she flees to the shrine of her god, only to find that even her god is unable to aid and defend her.

Shall come to his sanctuary - This refers to his “principal” sanctuary, or the temple of the principal god they worshipped—the god “Chemosh” (1 Kings 11:7). This does not mean the temple at Jerusalem, though Kimchi understands it that way, but rather the temple of the chief divinity of Moab. Jerome says that this temple was on Mount Nebo.

Shall not prevail - That is, her prayer shall not be heard.