Cast the First Stone

This comes directly from the Gospel of John, chapter 8. Religious leaders bring a woman accused of adultery to Jesus, reminding him that the law demanded she be stoned, and challenge him to judge her. His response: "He that is without sin among you, let him first cast a stone at her." One by one, her accusers leave without throwing anything, apparently unable to claim they were sinless themselves. The phrase has survived as a compact way of saying: don't condemn others for faults you share, or haven't examined in yourself first.