Jamieson, Fausset and Brown on James 2:5

5. Hearken--James brings to trial the self-constituted "judges" (Jas 2:4).

poor of this world--The best manuscripts read, "those poor in respect to the world." In contrast to "the rich in this world" (1Ti 6:17). Not of course all the poor; but the poor, as a class, furnish more believers than the rich as a class. The rich, if a believer, renounces riches as his portion; the poor, if an unbeliever, neglects that which is the peculiar advantage of poverty (Mt 5:3; 1Co 1:26, 27, 28).

rich in faith--Their riches consist in faith. Lu 12:21, "rich toward God." 1Ti 6:18, "rich in good works" (Re 2:9; compare 2Co 8:9). Christ's poverty is the source of the believer's riches.

kingdom ... promised--(Lu 12:32; 1Co 2:9; 2Ti 4:8).