It is pretty easy to get trapped into wondering in what way the followers of Jesus, who are in part listed in the Beatitudes (Matt 5:3-12), are to be like salt and like light. Perhaps like salt we are to be preservatives or to enable purification or to add zest and taste to the meal. Perhaps like light we are to dispel darkness or to shine our lights on the sin of the world. Perhaps so and perhaps not.
My contention is this: Jesus does not exactly spell out how disciples are to be either like salt or like light. Instead, and here is the point as I see it: first, they are salt and they are light. They are not exhorted to be salty or to be enlightening. They already are salt and light. Saltiness and light-ness are attributes of Jesus’ disciples because they are following Jesus.

Second, the focus of the passage is on maintaining what they already are by not destroying what they are.
Thus, “you are the salt.” But, if salt becomes insipid it is useless. Implication: don’t let that happen. Thus, “you are the light.” But, if you hide your light under a bushel the light is covered up. Implication: don’t let that happen.
So, the disciple of Jesus is one who simply stays salty and stays bright.
Finally, the passage speaks directly about the importance of “good deeds” and how they have an inevitable impact on the environment and how good deeds can provoke others to praise God.
To be salt and to be light most likely then means that the disciple of Jesus is to be a person who is full of good deeds, who also consistently is full of good deeds, and so draws attention to the Kingdom work of God.
In other words, this passage is a summons for the followers of Jesus to let the story of God be told in their own lives in such a way that others see the story performed and seek to be incorporated into that story.
When I think of salty and light-type folk I think of Augustine, and St. Benedict, and St. Francis, and Luther/Calvin/Zwingli, and Menno Simons, and the Wesleys. I think of St. Macrina and Teresa of Avila and Catherine of Siena. I can think of many more, and so can you. A picture of Bonhoeffer evokes a story of grace and faithfulness and spiritual vigor. The picture is a story.
When you think of them you say to yourself, “I know that story.”