John Calvin on James 4:15

15 If the Lord will. A twofold condition is laid down, “If we shall live so long,” and, “If the Lord will;” because many things may intervene to upset what we may have determined; for we are blind as to all future events. The words may be rendered thus, “If the Lord will, we shall both live and do this or that.” So that living and doing are both dependent on God’s will. By will he means not that which is expressed in the law, but God’s counsel by which he governs all things.