Thy sun … thy moon. That which is to thee instead of sun and moon—Jehovah's brightness. The days of thy mourning shall be ended. Till the new Jerusalem descends from heaven (Revelation 21:2), and Christ reigns personally over his people (Revelation 22:5), the Church is always, more or less, in a state of mourning.
The Bridegroom is away (Matthew 9:15); his light shines upon his Church only by snatches; his Church feels itself unworthy of him—cold, unloving, stained with sin. Fasting, weeping, and mourning befit such a state of things.
But in the final condition of the redeemed their mourning shall be ended, "sorrow and sighing shall have fled away" (Isaiah 35:10); God shall have "wiped away all tears from their eyes" (Revelation 21:4); "There shall be no more death" (Revelation 21:4); "no more curse" (Revelation 22:3); "neither sorrow, nor crying; neither shall there be any more pain: for the former things are passed away" (Revelation 21:4).
The days of mourning shall be ended.