John J. Pilch provides a reference which supports what I read in the Social-Science Commentary on the Synoptic Gospels (Malina, Rohrbaugh). I am amazed that I never recall reading or hearing this about salt. As I looked at my three commentaries and two study bibles what I saw was the usual. Salt evokes many connotations. One popular one is that it is an enhancer of flavor and that Christians are to be bring "zest" to the earth. Boring (New Interpreter's Bible, p 181) lists sacrifice, covenant loyalty, fellowship, purification, and preservation in addition to seasoning (each with bibical references with verse and chapter)
Jews cooked with dung mixed with salt. When the salt plates stopped burning they were tossed out (in the parallel from Luke it says "not fit for the dunghill" which makes sense to me now). This added meaning may indicate Jesus' primary reference, but certainly the image of "y'all are salt" is meant to be multi-dimensional. Jesus was the master of parables, and parables are meant to take us deeper (and in many directions). The plural (y'all) is a reminder that being salt is a corporate task. I also am more intentionally aware that Jesus is talking to Jews. He is the Messiah telling Jews who are His followers that their vocation (as Jews) is to be salt (and light--more on that). The Jewish self understanding, found over and again in their Bible, is a vocation. Jesus confirms the truth of this and affirms actively seeking to be faithful in this ministry. Too often we are content to be on the sidelines failing to function as salt. Often times, a (pseudo-) pietistic humility leads us to negate our vocation by saying "we are nothing special." In the first place, this is ignoring the communal component--Jesus is not saying it is "all about me." He is saying it is all about us, we are the salt. It is a fine line between humble faith and humble unfaithfulness. Jesus says "You folks are salt" and my guess is He means it. If some theologies would like to deny this as too man-centered so be it, but their problem is with Jesus' teaching (and as He is Lord I prefer to conform to Him!). I think Jesus take seriously the power within each human person to choose and act. Obviously, He was aware of sin and weakness (as John's Gospel tells us, "He was reluctant to trust Himself to the crowds because no one needed to tell Him about the human heart"). Jesus knows that we are in need of God's help, but He also knows tells us, over and over, that we have responsibility. Why wouldn't He, isn't that a major part of the Jewish religion? Grace and salvation are Jewish to the core, but so is the call to faithfulness and loyalty to the merciful YHWH Father who has shown us such undeserved kindness.
Light is present at the beginning of creation. The separation of light and dark is existential. In our world of electricity and ambient light it is hard to understand how dark dark would be in the ancient world. The emotional value of darkness was compounded by the association with Satan and the demonic. Most of us still have some primordial fear of the dark, even if less terrified than in our youth. In Exodus 10 God uses darkness as a 'sign' of His presence in Egypt, though Israel has light. And in Exodus 13 Fire of God serves as a night light. Judgment and Salvation, darkness and light. Numerous passages of the Torah explain the requirement to keep light burning in the Temple. (In our church we do the same as a sign of Jesus present in the reserved eucharist).
Psalm 4:6 "lift up the light of your countenance upon us O God"
Psalm 18:28 "Yea, thou dost light my lamp; the LORD my God lightens my darkness."
Psalm 27:1 "The Lord is my light and my salvation, whom shall I fear?"
Psalm 43:3 "Send out your light and your truth..."
Isaiah 2:5 "let us walk in the light of the Lord"
There are dozens more references to God as light, His word as a light for our path, and other uses of the image. For our purposes, however, it seems most likely that Jesus is making reference to
Isaiah 42:6"I am the LORD, I have called you in righteousness, I have taken you by the hand and kept you; I have given you as a covenant to the people, a light to the nations..."
The nations are the Gentiles. Jews were chosen by God the be a light shining, a perpetual witness, to a fallen world under the spell of darkness. Whatever else we are as Christians, it is an extension of the mission given to Abraham's children. In the Messiah, we are not Jews but share in the Jewish birthright. We become adopted children.
The purpose of the "good deeds" which manifest the light is to glorify God. No "filthy rags" here. As always, the Bible has a "rest of the story." Certainly, there is nothing we humans can do which is worthy of God (hence 'filthy rags' theology), but like any parent, God appreciates our efforts in the context of our limitations. Our five year old's hand drawn card is beautiful to us for reasons other than artistic. As children of God we are imitators of God. The one thing we can do is be motivated by the desire to glorify Him. In the end, I believe that "Jesus is the light of the world." Only Jesus can be. He is the sun. We, however, like the moon, can reflect His light. It is our job to do that. The light is not generated by us or in us, but it is a bright light none the less. The more we seek to give God glory, the more that light shines. It is all we who love the Lord can do. All things come from Him, we only return what is His. I conclude with a word from St. Diadochos of Photiki (Philokalia, p. 256) from the 5th Century. Ironically I read it this morning in my personal prayer time.
"I know a man who love God with great intensity, and yet grieves because he does not love Him as much as he would wish. His soul is ceaselessly filled with burning desire that God should be glorified in him and that he himself should be as nothing. This man does not think of what he is, even with others praise him. In his great desire for humility he does not think of his priestly rank, but performs his ministry as the rules enjoin. In his extreme love for God, he strips himself of any thought of his own dignity; and with a spirit of humility he buries in the depths of divine love any pride to which his high position might give rise. Thus, out of desire to humble himself, he always sees himself in his own mind as a useless servant, extraneous to the rank he holds. We too should do the same, fleeing all honor and glory in the overflowing richness of our love for the Lord who loves us so greatly."
We should all do the same. Love God and seek His glory, His alone. It is the role of the church. It is salt and light. It is the only way to live!