Matthew 5:13–20: In verse 11 the address of Jesus shifted from the third to the second person: “Blessed are you.” The addressed party is the Church—or rather, the Christians—inasmuch as the number of the address is plural. That plural, addressed to Christians, is maintained in the verses now under consideration: “You are the salt of the earth,” this section begins, and it ends, “for I say to you (verse 20).
We start with the metaphors of salt and light, both of them referring to Christians. In each case the beneficiary of these two blessings is the earth (ge) or World (kosmos), meaning those who are not Christians (verse 13). Salt and light describe the very people that the world persecutes and maligns (verses 11–12). No amount of persecution justifies the forfeiture of the Christian vocation to be salt and light to the rest of humanity. Neither salt nor light exist for themselves. Should Christians fail in this vocation, they are no longer of any use. They are to be “thrown out,” like the tares (13:40) and the inedible fish (13:48).
The metaphor of light on a lamp stand is transformed into a city seated on an acropolis, where it is visible to everyone (verse 14). Neither can Christians be concealed if they do the “good works” (ta kala erga) that their heavenly Father expects of them (verse 16). Those who see these good works belong to the same “earth” or “world” that persecutes the Christians. The world is to be enlightened by the very people it persecutes.
What Matthew has in mind here is the Christian vocation to holiness, by which the world is instructed in the ways of God. This holiness, according to the present passage, pertains to the missionary mandate of the Church. It is the way the Church shares the Gospel with “all nations” (28:19–20). This is the light that shines on those sitting in darkness (4:16).
The connecting link of verses 13–16 with the rest of the Sermon on the Mount is “your Father in heaven” (verse 16). This reference will become a leitmotif in the following chapter.
The rest of chapter five, starting with the present verses, is concerned with Jesus’ relationship to the Old Testament Law. This theme is related to the metaphors of salt and light through the continuity linking the Church to ancient Israel, the legitimate continuation of God’s redeemed people. It is the Church that continues Israel’s vocation to “salt” and illumine the world. For this reason it is imperative to speak of the Church’s relationship to the Torah, and this relationship is the subject of the rest of the present chapter.
Matthew has already begun to say a great deal about Jesus’ fulfillment of biblical prophecy. Now he starts to speak of Jesus’ fulfillment of the Law. Indeed, the word “prophets” in the present passage (verse 17) does not refer to the fulfillment of biblical prophecies in the Old Testament. It refer, rather, to the prophets in their role as interpreters of the Law—the prophets as moral teachers. The sense of this verse, then, is that Jesus completes, or brings to fulfillment, the moral doctrine of the Law and its continuation in the Prophets. Throughout the rest of this chapter, therefore, Matthew speaks simply of the Law, not mentioning the Prophets again.