Grant Osborne in his commentary on Matthew says one of the applications we learn from Matthew 5:13-16 is that discipleship is always active. Being salt and light is not only witnessing or confronting evil but a lifestyle full of “good works,” always helping, always demonstrating God’s love and concern for the world. Focusing on salt’s ability to flavor, as we act as salt, we let others taste the goodness of God. As a visible city or a lamp on a stand, we let others see the goodness of God.

That’s why Jesus’ words about salt imply a judgment. Jesus does not want a useless disciple, one so diluted or polluted by the world, that our effectiveness as salt is gone. We are only fit for the garbage heap if that’s how we are! True discipleship is distinguished by the number of people affected by it.

Jesus is also calling us to a visible discipleship. The city is not hidden; the lamp is not under a basket; the light shines before others. We cannot follow Jesus in a purely private way and think we are behaving as citizens of the kingdom. Dietrich Bonhoeffer said in his book Discipleship, “Any community of Jesus which wants to be invisible is no longer a community that follows him.” We shine before others so that others may see our good works and give glory to our Father.

“Fulfilling this plan [to be salt and light] will demand that the whole of our lives be whole-heartedly and unceasingly devoted to him and to his service. That devotion will cost us everything.” (Sinclair Ferguson)