5:1-6 Public troubles are most grievous to those who live in pleasure, and are secure and sensual, though all ranks suffer deeply at such times. All idolized treasures will soon perish, except as they will rise up in judgment against their possessors. Take heed of defrauding and oppressing; and avoid the very appearance of it. God does not forbid us to use lawful pleasures; but to live in pleasure, especially sinful pleasure, is a provoking sin. Is it no harm for people to unfit themselves for minding the concerns of their souls, by indulging bodily appetites? The just may be condemned and killed; but when such suffer by oppressors, this is marked by God. Above all their other crimes, the Jews had condemned and crucified that Just One who had come among them, even Jesus Christ the righteous.
3. is cankered—"rusted through" [Alford].
rust … witness against you—in the day of judgment; namely, that your riches were of no profit to any, lying unemployed and so contracting rust.
shall eat your flesh—The rust which once ate your riches, shall then gnaw your conscience, accompanied with punishment which shall prey upon your bodies for ever.
as … fire—not with the slow process of rusting, but with the swiftness of consuming fire.
for the last days—Ye have heaped together, not treasures as ye suppose (compare Lu 12:19), but wrath against the last days, namely, the coming judgment of the Lord. Alford translates more literally, "In these last days (before the coming judgment) ye laid up (worldly) treasure" to no profit, instead of repenting and seeking salvation (see on Jas 5:5).