Invasion and war had already overtaken Jerusalem when Jeremiah wrote this lament, but more destruction was to come (v. 9).
15:5 The Lord said that no one would have pity on Jerusalem when she had experienced His judgment (cf. Lam. 1:1, 12, 21; 2:13, 20).
15:6 The city had forsaken Yahweh. It had regressed rather than advanced morally and spiritually. The Lord promised to destroy her with His own power. He was tired of returning to a people who implored Him not to leave them (14:9). He was weary of waiting to judge a people who had grown weary of repenting (9:4).
15:7 He would also scatter the people of the outlying towns, as when a farmer winnows his grain by throwing it up to the wind that blows the chaff away (cf. Matt. 3:12). Children would die because God's people did not repent. Former winnowings, like the exile of the Northern Kingdom in 722 B.C., had not brought the Judahites to repentance.
15:8 So many young men of military age would die that the land would be full of widows who would mourn the deaths of their sons (cf. 2 Chron. 28:6). This judgment would constitute a setback in the promise to multiply Abraham's descendants as the sand of the sea (Gen. 22:17).
15:9 The woman who had a perfect family and complete happiness would become so sad that she would hardly be able to breath (cf. 1 Sam. 2:5; Ruth 4:15). It would be as though the day of her rejoicing ended at noon. Her sun disappeared at noon with the death of her sons. She would have no heirs and comforters in her old age (cf. 14:3-4). It is possible that Jeremiah was personifying Jerusalem and or Judah as a widow, but a literal fulfillment is also probably in view (cf. Matt. 23:37-38; Luke 23:28-31).
The swords of the enemy would also devour many survivors of earlier invasions. This seems to indicate that one invasion of Jerusalem had already occurred when Jeremiah wrote this prophecy, probably the one in 597 B.C. (cf. 2 Kings 24:10-17).