James 5:1-6

The address at the beginning of the Epistle helps not a little to account for the peculiarity of the denunciation of the rich with which our chapter opens, as well as other passages afterward and before it. If directed to the twelve tribes that are in the dispersion, there is no difficulty; if it contemplated like Peter's two Epistles only such as are saints, not a little would sound harsh, to say the least. But as the inspired writer was led to take wider ground from the start, the true key of interpretation is put into our hands thereby.
“Come then, ye rich, weep howling over your miseries that are coming on. Your wealth is corrupted, and your garments are become moth-eaten. Your gold and your silver are rusted through, and their rust shall be for a witness to you, and shall eat your flesh as fire. Ye laid up treasure in [the] last days. Behold, the hire of the laborers who reaped your fields, that is kept back of you, [or, from you] calleth out; and the cries of those that reaped entered into the ears of Jehovah of hosts. Ye lived luxuriously on the earth and indulged yourselves; ye nourished your hearts in a day of slaughter. Ye condemned, ye slew the just one: he doth not resist you” (vers. 1-6).
The day of the Lord could not but be prominent before a godly Israelite imbued with the reiterated warnings of the prophets; and it is still hanging over man on the earth. The covenant people of old were prone to regard themselves as exceptions; but for their delusion they had no warrant or even excuse from scripture. The more privileged, if faithless, are the more guilty. “You only have I known of all the families of the earth; therefore I will punish you for all your iniquities.” The gospel brings in grace, and through faith deliverance; but the moral principles of divine government are immutable. God's wrath is revealed from heaven against all ungodliness, and unrighteousness of men that hold the truth in unrighteousness.
The poor are sinners no less than the rich; each have their special snares and dangers. But it is far harder for a rich man than for a poor to follow Christ truly. Therefore, said He to His disciples, “Verily I say to you, It is hard for a rich man to enter into the kingdom of the heavens. And again I say to you, It is easier for a camel to enter through the eye of a needle than for a rich man to enter into the kingdom of God.”
Here however they in a general and unsparing way are warned solemnly of their miseries that are coming on. The reader may profitably compare Isa. 2:77Their land also is full of silver and gold, neither is there any end of their treasures; their land is also full of horses, neither is there any end of their chariots: (Isaiah 2:7) to the end: only idols are not set forth by the Epistle as in the prophecy. But that day will deal with every one that is proud and lofty, and with every one that is lifted up, with every high tower, and every fenced wall, with all the ships of Tarshish and with all pleasant works of art. God is against their cherished wealth, and their endless store of raiment. To his eye that saw under the surface all was corruption, their gold and silver rusted throughout, the rust a witness to them and to eat their flesh as fire, The selfish unbelief that laid up treasures in closing days was no trifle in God's sight.
But they are charged with wanton cruelty and fraud in their dealings with the laborers who reaped their fields. Their very wealth tempts the rich to withhold payment of wages to the poor; their own things are alone of moment in their eyes, while they postpone to a convenient season the claims of such as live from hand to mouth. But the debt cries aloud to Him Who ever feels for the poor, as He showed Who alone made Him fully known. Yes, the cries of the reapers, which may not have reached the rich, entered into the ears of the Lord of hosts, and His blow would fall when least expected.
The rich are next arraigned for their luxurious living on the earth, as if the God of heaven regarded it not. In a world of wretchedness and want, they indulged themselves, as if they were not stewards and had no account to render; they nourished their hearts in a day of slaughter, as heedless as the beasts slain for food of man.
Another charge follows, still more tremendous: “Ye condemned, ye slew the just one: he doth not resist you.” This made their guilt less excusable. “He did no sin, nor was guile found in his mouth; who, when reviled, reviled not again, when suffering, threatened not, but gave [himself] up to him that judgeth justly.”