Midrash su Ecclesiaste 10:10

R. Ami said again: "What is the meaning of the passage (Ecc. 10, 10) If the iron be blunt, and man do not whet the edge, then must he put to more strength; but wisdom is profitable to direct. This signifies that when thou seest that the sky is as dark as heaven and yet does not send down dew or rain, know that it is because of the persistent wickedness of the generation; as it is said, and man who did not whet the edge [of righteousness]. What is the remedy for such an evil? To make strong appeals for mercy; as it is said: Then must he put to more strength. But wisdom is profitable to direct, means so much the more will they be granted mercy if at the beginning their deeds were those of wisdom."