In many places of Bible it is written that our purposes are for the heavenly life, for soul, spiritual things etc.

So a natural question arises: Why us not to destroy our bodies as these are not important.

The answer to this questions is (1Cor. 3:16) 16 Don’t you know that you are a temple of God, and that God’s Spirit lives in you? 17 If anyone destroys the temple of God, God will destroy him; for God’s temple is holy, which you are.

Now we know that we should not destroy our bodies, but not because these would be important or valuable for us (these are not important for us at all as we are for heavenly life not for the Earth), but just to not be punished for damaging a temple.