“And he observed mourning for his father seven days” – why are seven [days] observed? It is corresponding to the seven days of the wedding feast. The Holy One blessed be He said to them: ‘In this world, you were sorrowful with this righteous one and observed mourning for him for seven days. In the future world, I will transform that mourning into rejoicing, as it is stated: “I will transform their mourning into gladness, and I will console them and cheer them from their sorrow” (Jeremiah 31:13).
Just as I comfort you, so I will comfort Zion and all its ruins, like the matter that is stated: “For the Lord will comfort Zion; He will comfort all her ruins; He will render its wilderness like Eden and its desert like a garden of the Lord. Gladness and joy will be found in it, thanksgiving and the sound of music”’ (Isaiah 51:3).