Commentaries:
Anyone who causes a Christian who manifests this childlike attitude to sin, or who places anything in his way to impede his faithfulness, would be better off being weighted down and thrown to his death into the sea. It would be better for him to die before committing such a sin. Christ regards injuring or causing a weak Christian to sin as a very serious offence (Romans 14:19-23; I Corinthians 8:9-13). We are all human, so offences will happen, but our Savior pronounces woe on the person who offends and causes others to sin. Anyone who leads others into sin bears great guilt. Only a deep-seated wickedness attempts to confuse and destroy another's potential.
Martin G. Collins
Parables of the Millstone and the Lost Sheep