4:21 The Edomites, kinsmen of the Judahites, were rejoicing over Judah's destruction (cf. Ps. 137:7; Jer. 49:7-22; Ezek. 25:12-14; 35), but the same fate was sure to overtake them (Deut. 30:7). They would have to drink the cup of Yahweh's judgment and would lose their self-control and self-respect.
"After the fall of Jerusalem in 587 BC, Nebuchadnezzar allotted the rural areas of Judah to the Edomites as a reward for their political neutrality, and as a recognition of the active help which they had provided for Chaldean military units during the final days of the campaign (cf. Ezk. 25:12-14; Ob. 11-14)."53
The land of Uz, Job's country, was either a part of or another name for Edom (cf. Job 1:1).
4:22 Jerusalem's punishment had reached its end; the exile would not last forever. But God would yet punish Edom for her sins.
"Chapter 4 does not end with a prayer, as do the preceding chapters, but it is followed by a prayer--all of chapter 5."54