Jas. 4:13. Come now, you who say, "Today or tomorrow we will go to such and such a city, spend a year there, and buy and sell and make a profit";
He does not destroy free will, but shows that not everything depends on man himself — the grace from above is also needed, for one may run about, and trade, and do everything necessary for life, but one must ascribe this not to one's own labors, but solely to the lovingkindness of God. Jeremiah also says: "O Lord, I know the way of man is not in himself" (Jer. 10:23), and the author of Proverbs: "Do not boast about tomorrow, for you do not know what a day may bring forth" (Prov. 27:1).
Jas. 4:14. whereas you do not know what will happen tomorrow.
He shows the vanity of our life and puts us to shame for spending our entire life in vanity, for all our labor is exhausted on temporal evil. David says the same: "Surely every man walks about like a shadow; surely he busies himself in vain" ("Truly, man walks about like a phantom; in vain he bustles") (Ps. 39:6) — that is, he busies himself over what does not exist but appears as if in a shadow, or over what has no independent existence but constitutes merely a likeness and image of a truly flourishing life.
Jas. 4:14. For what is your life? It is even a vapor that appears for a little time and then vanishes away.
Jas. 4:15. Instead you ought to say, "If the Lord wills, we shall live and do this or that."
Vapor is a dark compound arising from intense heat and moisture and having the briefest existence, for on account of its extreme fineness it quickly "vanishes" from contact with its surroundings, entering into them and dissolving, just as a small portion of moisture dissolves in water. This is what the apostle likened our "life" to, and most fittingly. Having interrupted the discourse midway with this comparison, he returns to it again and continues. Here is the connection: "Come now, you who say, 'Today or tomorrow we will go to such and such a city, spend a year there, and buy and sell and make a profit'" (Jas. 4:13)... "Instead you ought to say, 'If the Lord wills, we shall live and do this or that'" (Jas. 4:15).
Having interrupted the connection of the discourse with the example by which the apostle wished to show more strikingly the vanity of worldly cares proceeding from pride, he then adds what was omitted. The course of the speech is this: "You, in your arrogance, boast." Who? "You who do not know what will happen tomorrow, for what is your life..." and so forth. With the words "what is your life?" he prepared for himself the way to this subtle precept; then he adds the instruction itself, doing so most appropriately.
Jas. 4:16. But now you boast in your arrogance.
The proud person and pride occupy themselves with unreal things, which is why the proud one is so called — meaning "one living in delusion or deception."
Jas. 4:16. All such boasting is evil.
"All such boasting is evil."
Jas. 4:17. Therefore, to him who knows to do good and does not do it, to him it is sin.
He again takes up the subject of vain arrogance, which usually arises from pride, and as if concluding the discourse, says that boasting is evil. If it is evil, then it proceeds without doubt from the evil one. But those who through holy baptism have given themselves over to the Lord should not accept what is sown by the evil one. He adds also this: "to him who knows to do good and does not do it, to him it is sin" (Jas. 4:17). Again he admonishes the false teachers not to dare to teach what they themselves have not first practiced, for blessed, it is said, is not the one who teaches, but the one "who does and teaches" (Matt. 5:19), since deeds must precede words, by which the righteous man also proclaims the faith he manifests. For whoever, says the Lord, breaks one of these least commandments and teaches men so — that is, teaches that which he himself has not labored at — shall be called least... "but whoever does and teaches them, he shall be called great" (Matt. 5:19). Therefore the God-man Himself first began to do and then to teach (Acts 1:1). Such, in my opinion, is the thought also in these words: "He who glories, let him glory in the Lord" (1 Cor. 1:31) — that is, as one like the Lord, having in Him a teacher and example. Similarly, David says: "In the Lord shall my soul boast" ("My soul shall make its boast in the Lord") (Ps. 34:2) — saying nothing other than this: I would wish to boast in that I walk according to the commandments of the Lord.