R’ Yehudah said further: In a synagogue that has been destroyed one may not offer eulogies therein, twist ropes therein, spread nets therein, spread produce on its roof, nor use it as a shortcut —- for the Torah states, And I shall make desolate your sanctuaries; [this implies that] they are holy even when they are desolate.  If grass grew [in the ruins], one may not detach it, because of grief.