The night-weeping of exile finds its scriptural anchor in Eichah 1:2, where Jerusalem is depicted weeping bitterly in the night with tears on her cheeks and no comforter, and Yalkut Shimoni on Nach 1007 amplifies this by teaching that one who weeps in the night is joined in lamentation by the very walls of the house and the constellations of the heavens — a cosmic solidarity in grief.
The darkness of exile and its attendant weeping are not, however, the final word: Ein Aya, Berakhot 9:252 teaches that the exile resembles night and the redemption resembles day, with dawn — the gradual lightening — standing between them, just as the sages compared Israel's salvation to the dawn that brightens little by little, so that even the intensified suffering felt at the threshold of redemption is itself a sign of approaching light.
This movement from darkness toward light rests on Israel's inner nature: Ein Aya, Shabbat 9:75 holds that the natural inner essence of Israel is the light of God within their souls — a joy of worlds and an inner holy delight — and that this content can never be permanently lost, only hidden, so that the accumulated waves of suffering and historical experience will ultimately restore Israel's natural character and extend to them the light of return.
The repair that emerges from the bitterness is described in Orot HaTeshuvah 3:5, where out of precisely this inner bitterness repentance comes as the prescription of a faithful healer, suffusing the person with a spirit of grace and consolation — 'as a mother comforts her child, so will I comfort you' (Yeshayahu 66:13) — until his face shines and his eyes fill with a holy fire.