Dedicated to the Lord Jesus Christ Who loved us, gave Himself for us, and washed us from our sins in His own Blood; and to the Church, which is His body.

MATTHEW 5:23-30
Jesus isn't suggesting dismembering our bodies. He is drawing on the drive within everyone of us of self preservation to make a point. If we value our body enough that we would never sacrifice one of its parts, then we should honor our spiritual well being much more.
Ever since Adam and Eve, all of our priorities have been misplaced. Great effort is put into preserving our physical life while our spiritual condition is overlooked. It constantly gets put aside while we tend to more urgent matters of this life.
Our bodies are just temporary. If we live 70 years or more, that is just a fraction of a second in the light of eternity. Our spiritual man lives forever. The state in which it exists is determined by choices made in this life.
We must choose to make our spiritual condition our top priority, by spending more time on our spiritual well being than we do our physical well being.