James wants planners who leave God out to feel how fragile their plans are. They spoke with confidence about a whole year, yet "ye know not what shall be on the morrow." Barnes says, "They formed their plans as if they knew"; James says it cannot be known. The question "what is your life?" asks them to look at the very thing every plan depends on. Barnes draws the point from James' picture: "Who can calculate on the permanence of a vapor?"

James answers at once: "It is even a vapour, that appeareth for a little time, and then vanisheth away" (James 4:14). Then he tells them what to say instead: "If the Lord will, we shall live, and do this, or that" (James 4:15). He warns that their boasting is evil (James 4:16) and ends, "to him that knoweth to do good, and doeth it not, to him it is sin" (James 4:17).

The traders in James 4:13 describe their plan: travel to a city, stay a year, trade, and make a profit. The word "vapour" is the Greek atmis, breath, steam, or vapor. Gill describes it as something that "rises out of the earth, or water, and expires almost as soon as it exists." He also points to Proverbs 27:1: "Boast not thyself of to morrow; for thou knowest not what a day may bring forth."

This question sets our short lives against God's sovereign will. James does not say planning is wrong. He says plans should be held under God: "If the Lord will" (James 4:15). Matthew Henry's Concise Commentary reflects on the vapour: "So short, unreal, and fading is human life."

The point is not gloom but trust. Because life is short and the future is unknown, the wise response is humble dependence on the God who holds tomorrow. The same chapter has already called for that humility: "Humble yourselves in the sight of the Lord, and he shall lift you up" (James 4:10).