In the first century, salt had two purposes in the Middle East. Due to the lack of refrigeration, salt was used to preserve food, especially meat which would quickly spoil in the desert environment.
Similarly, Jesus likens believers in Christ to preservatives of the world, preserving it from the evil inherent in the society of ungodly people whose unredeemed natures are corrupted by sin.
Second, salt as a flavour enhancer, enhances the flavour of the food it seasons. This reflects how the followers of Christ should stand out as those who “enhance” the flavour of life in this world. Christians, living under the guidance of the Holy Spirit and in obedience to Christ, will inevitably influence the world for good.
In the analogy of light to the world, the good works of Christ’s followers are to shine for all to see. The idea here is similar to the above since the appearance of light in darkness is unmistakable. The presence of Christians in the world must be like a light in the darkness so that those who looked on might “glorify your Father who is in heaven” (v. 16, KJV).
As we walk in the Spirit, our faith grows. Our good works and our attitude as a result of salvation help others to have that “saving” faith. This is what Paul reiterated in Philippians 2:12 that we should “work out our own salvation.”
When we wear our faith on our sleeve and we have the “mind of Christ” others will want to know about Jesus.