John Calvin on James 4:9

9 Be afflicted and mourn. Christ denounces mourning on those who laugh, as a curse, (Luke 6:25;) and James, in what shortly follows, alluding to the same words, threatens the rich with mourning. But here he speaks of that salutary mourning or sorrow which leads us to repentance. He addresses those who, being inebriated in their minds, did not perceive God’s judgment. Thus it happened that they flattered themselves in their vices. That he might shake off from them this deadly torpor, he admonishes them to learn to mourn, that being touched with sorrow of conscience they might cease to flatter themselves and to exult on the verge of destruction. Then laughter is to be taken as signifying the flattering with which the ungodly deceive themselves, while they are infatuated by the sweetness of their sins and forget the judgment of God.