The former is more likely, that is, that they were Christians oppressing their fellow believers. This is more likely because above, where the rich are mentioned (Jas 1:5, 9, 10, 27; Jas 2:2 and following; Jas 4:1 and following), Christians are likewise meant.
Yet there is no doubt that the speech has its full meaning also for unbelieving Jews. Such treatment of the poor by the rich (Jas 4:6) is contrary not only to the Christian law, but also to the Mosaic law.
In his speech against the hard-hearted rich, the Apostle first depicts the judgment of God coming upon them (vv. 1-3). Second, he characterizes their conduct as the ground or cause of the judgment that will be accomplished over them (vv. 4-6).
“Weep and howl for your miseries,” and so forth. These are not tears of repentance from awareness of one’s sins, as in Jas 4:9. They are tears of fear and terror before the face of the coming judgment of God in the miseries to come, as in Mt 24:30.
Of course, there is no doubt that the aim of such speech, as with the Old Testament prophets, is none other than to move hard hearts through such threats toward conversion to God and repentance.
“The Apostle makes them howl, that is, weep bitterly, because they store up their wealth for corruption and do not distribute it to the poor. For wealth does not perish only when it is spent on the poor” (Theophylact).
“For your miseries that are coming upon you,” that is, for the miseries that will overtake you and are coming upon you.
The speech is not about the natural fate of every earthly wealth, as corruptible and quickly passing (Jas 1:10 and following; Jas 4:14). It concerns the fate that will befall the rich as the judgment of God, as a special punishment of God.
The particular forms of this punishment are depicted further on. What is this judgment that expresses itself in the miseries of the rich?
The following expressions point to it: “in the last days” (v. 3), the coming of the Lord, and indeed near (vv. 7 and 8), and “the Judge is at the doors” (v. 9). It is precisely the judgment that will take place at the approaching coming of the Lord.
From these indications the speech receives a purely New Testament character. Yet the particular features of the depiction of this judgment may also be found in the Old Testament prophets, as we shall see further.
In what sense the Apostle speaks of these miseries as already coming, that is, of this judgment and this coming of Christ as already near, as the other apostles also speak in the same sense, see the notes on Jas 5:7, 8, 9 and parallels.