Ecclesiastes 3:3

To kill. Commentators disagree as to whether Solomon here refers to war or to other circumstances. It is possible that he is speaking of the execution of criminals, and of measures for the protection of threatened communities. Or he may be thinking of an injured domestic animal, and the fact that the extent of injury must determine whether it is more merciful to put the creature out of its misery or to attempt to “heal” it.

To break down. There is a time when buildings must be demolished and more convenient ones put up in their stead. For millenniums it has been a common habit in the Near East to utilize the ruins of one civilization as building materials for the new. Solomon may here refer to his own great building projects.