God sent His disciples to "season" the earth. As believers, we are to "season" mankind with knowledge and grace acceptable to God. Our thoughts and affections, as well as our words and deeds should all be seasoned with the salt of grace. However, salt without its taste is not good or useful.
We should also be a light to those who are in darkness. Our light will shine when we do good works so that others may see Christ in us. These works are not for our personal glorification, but to glorify our Father who is in heaven.