Albert Barnes Commentary James 5:18

"And he prayed again; and the heaven gave rain, and the earth brought forth her fruit." — James 5:18 (ASV)

And he prayed again. The allusion here seems to be to 1 Kings 18:42, 45, though it is not expressly stated there that he prayed. Perhaps it might be fairly gathered from the narrative that he did pray, or at least that would be the presumption, because he put himself into a natural attitude of prayer: he cast himself down upon the earth, and put his face between his knees, (1 Kings 18:42).

In such circumstances, it is to be fairly presumed that such a man would pray. However, it is remarkable that this is not expressly mentioned, and quite as remarkable that James should have based his argument on something that is not expressly mentioned but seems to have been a matter of inference.

Therefore, it seems probable to me that there was some tradition on which James relied, or that it was a common interpretation of the passage in 1 Kings 18 that Elijah prayed earnestly, and that this was generally believed by those to whom the apostle wrote. No one could doubt the fact that Elijah was a man of prayer; and in these circumstances, the tradition and common belief were sufficient to justify the argument used here.

And the heaven gave rain. The clouds gave rain. The heaven was black with clouds and wind, and there was a great rain, (1 Kings 18:45).

And the earth brought forth her fruit. The famine ceased, and the land again became productive. The case referred to here was indeed a miracle, but it was a case of the power of prayer and therefore relevant. If God would work a miracle in answer to prayer, it is reasonable to presume that He will bestow upon us the blessings we need in the same way.