Christians are called to have an impact on the reality in which we live. When you turn on a light, wait for the darkness to recede. When we salt something we are mineralizing it and conserving it. In this sense the disciples of Jesus are sent to the world for something and our presence in the middle of the world can not go unnoticed because we are, by God's grace, bearers of an immense gift: the Good News of Jesus Christ.
Thanks for sharing @joelfer