Sodium is an extremely active element found naturally only in combined form; it always links itself to another element. Chlorine, on the other hand, is the poisonous gas that gives bleach its offensive odour. When sodium and chlorine are combined, the result is sodium chloride--common table salt--a substance vital for our body (in the right quantity).
Love and truth can be like sodium and chlorine. Love without truth is flighty, sometimes blind, willing to combine with various doctrines. On the other hand, truth by itself can be offensive, sometimes even poisonous. Spoken without love, it can turn people away from the gospel. When truth and love are combined in an individual or a church, however, then we have what Jesus called "the salt of the earth," and we're able to sustain and bring out the beauty of our faith.