Matthew Poole and continuators on 1 Kings 18:42

42 So Ahab went up to eat and to drink, and Elijah went up to the top of Carmel , and he cast himself down upon the earth, and put his face between his knees ,

Where he might secretly and ardently pour out his Prayers unto God; and whence he might look towards the Sea, and discern when the Rain was coming.

He either sate, or rather, kneeled upon his Knees, and then cast down his Face to the Ground between his Knees; either, in token of profound reverence and humility; or, out of fervency of spirit, which oft disposeth men to uncouth gestures, which at other times, or in other men, would be ridiculous; but in them and in that case, are usual and allowed; or, that turning away his Eyes from all outward objects, he might be more intent and earnest upon his work, or pray to God without distraction.