Matthew 5:29

And if thy right eye causeth thee to stumble, pluck it out, and cast it from thee: for it is profitable for thee that one of thy members should perish and not thy whole body be cast into hell.

The location of this verse in the midst of Jesus' teaching on adultery makes the meaning clear. Christ expects his followers to avoid gross sin by keeping the fountain of the heart sweet and clean. That this requires exertion, self-denial, and determination of heroic proportions is seen in the implied comparison of plucking out the right eye. The comparison is valid and is so recognized in medicine which often amputates an offending member to save the entire physical body. The giving up of cherished sin is far more difficult but just as necessary for those who would truly enter into life. See under Matthew 18:8-9.