Salt and light
Salt and light are metaphors used by Jesus in the Sermon on the Mount, one of the main teachings of Jesus on morality and discipleship. These metaphors in Matthew 5:13, 14, 15 and 16 immediately follow the Beatitudes and refer to expectations from the disciples.
The first verse of this passage introduces the phrase "salt of the earth":
Ye are the salt of the earth: but if the salt have lost its savor, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out and trodden under foot of men.
Ye are the light of the world. A city set on a hill cannot be hid. Neither do [men] light a lamp, and put it under the bushel, but on the stand; and it shineth unto all that are in the house. Even so let your light shine before men; that they may see your good works, and glorify your Father who is in heaven.