Gibbs, Jeffrey A. “Matthew 5:13-16: Summary of the Disciples’ Calling: Salt and Light.” St. Louis: Concordia Publishing House, 2006, pp. 257-262.
In Matthew 5:13 and 14, Gibbs sees the pronoun “you” to be very emphatic, referring to “you” and no others. The disciples are those who have a specific “beneficial effect...on the world” (Gibbs 2006, 257). Gibbs is clear that the thing which could lose its flavor is not the salt, but the world. The emphasis is on receiving the seasoning, not becoming or remaining salty. Gibbs discusses the BDAG entry and the content at some length (Gibbs 2006, 258).
Gibbs notes that Jesus describes the disciples as salt and light, using the indicative mood (Matt. 5:13-16). This is their identity. It is not a matter of possibility (Gibbs 2006, 259). The metaphor, according to Gibbs, introduces the rest of the sermon. As an introduction, he suggests the metaphor should not be pressed too hard. It will be unpacked in the sermon (Gibbs 2006, 259). The images are general in nature. Their role is to be a blessing to the world. All Christians, in one way or another, fulfill that role by their nature, rather than by tremendous works of virtue. However, Gibbs affirms that Jesus calls his people “to lives of remarkable purity, faithfulness, piety, love, and generosity” (Gibbs 2006, 261). It is the nature of the Christian to live a life which is remarkable in some ways.