John Calvin Commentary James 4:15

"For that ye ought to say, If the Lord will, we shall both live, and do this or that." — James 4:15 (ASV)

If the Lord will. A twofold condition is laid down: “If we live so long,” and, “If the Lord will,” because many things may intervene to upset what we may have determined; for we are blind to all future events. By “will” he means not what is expressed in the law, but God’s counsel by which he governs all things.