Being salt and light is all about relationships, isn't it? I mean when Jesus instructs us to be salt and light the implicit expectation is that you are salt and light TO someone or FOR someone. Often when we see these verses strictly about just making a difference in someone's life. While it is that, it is so much more. Throughout Jesus' teaching there is an assumption that we are in relationship with others. This is an overlooked part of this passage and the rest of Jesus' teaching.
When we speak of relationally what are we speaking of? I would like to propose that relationality is about two things: commonality and investment. When we have a relationship with someone we are at a very core theological level (ontologically) holding humanity in common. This common humanity is possible because Christ assumed all of humanity (all creation for that matter), affirmed it, and saved it. Our common thread, regardless of the salvific status of an individual is Christ's proactive salvific work. This work is actual and objective, not subjective. It creates a basis for a new reality that we all participate in at some level; perhaps not a salvific level, but an ontological and teleological level. This new reality and commonality is the basis for our relationship with others: our commonality is Christ's assumption of humanity. This commonality is really sacred. When we are being salt and light for and to others we need to remember that we aren't just "doing them a favor" or"sharing the Gospel with them" we are affirming our commonality. This commonality brings dignity to others. This dignity means that they are worth something. They should be more than a target for our evangelism as we were more than merely a target for God in Christ.
Building off of commonality we need to talk about investment. Investment is not a complex concept as commonality might be. When we are salt and light to and for someone we can only be so when we invest in their own person, their own reality (albeit void of a salvific component (?) ). We meet people where they are because where they are is as valid as where we are. Jesus modeled pouring Himself out as an offering for us (an investment for sure). We should model this by pouring ourselves out for those who we encounter.
In short, being salt and light is about relationships. We need to realize that we share both a commonality and based on the commonality we need to invest as Christ invested in others. As we practice commonality and investment we achieve the highest form of the Gospel and its message. People will see this and be compelled by the Gospel to accept Christ as both Lord and Savior.