Jesus said, "You are the salt of the earth."

In my opinion what "Salt" means is love. God's love dwells in us through Christ, and He has chosen to reveal that love to the world through us. Whoever we come in contact with, we are to love and be faithful to, to show kindness and mercy to, and console and sympathize with; to aid, support, encourage and help bear their burdens; also to forgive and bear all things, believe in and encourage, as well as weep with and rejoice with.

If we think "Salt" is "truth", and we are here to purify the world, and we are here as the worlds teacher, we elevate ourselves and extinguish the nature of Christ, which is gentle and lowly associating with the downcast. 

  If you bear the name of Christian and rely on the Bible and boast in God and say you know His will and approve the things that are essential, being instructed out of the Bible, and you are confident that you are a guide to the blind, a light to those who are in darkness, a corrector of the foolish, a teacher of the immature and have the Bible as the embodiment of knowledge and truth but fail to love, you have become "salt that has lost its savor, and are no longer good for anything except to be cast out and trampled under the foot of man."