Before condemning anyone who has done wrong, ask yourself whether your own conduct has been blameless.
The proverb derives from the story told in Chapter VIII of the gospel according to St John.
While Jesus was teaching in the temple the scribes and Pharisees brought before him a woman taken in adultery.
‘Moses in the law commanded that such should be stoned: but what sayest thou?’ they asked.
Jesus replied: ‘He that is without sin among you, let him first cast a stone at her.’
Those who heard this, ‘being convinced by their own conscience’, went out one by one until Jesus was left alone with the woman.
He asked her: ‘Woman, where are those thine accusers? Hath no man condemned thee?
‘No man, Lord.’
‘Neither do I condemn thee: go and sin no more.’