It is important for all Christians to let their lights shine because that is the way in which they can bear witness for God and bring others to the church and make productive use of their talents.
In the Gospel of Mark (Chapter 16, Verse 15), Jesus tells his disciples that they need to become missionaries. He tells them that the need to go out and to preach the gospel to the people of all nations. Most of us do not do this literally in the sense of going to a foreign land and trying to convert people to Christianity. However, this verse can apply to all Christians even so. When Christians let their lights shine, they are essentially proselytizing. They are showing by their example how Christians live and how it is good to be a Christian. If Christians do this properly, they can attract other people to the church. These do not need to be foreigners who have never heard the word of God. They can be Americans who do not have a faith or who have grown away from it. It is important to save them as well.
Thus, Christians are called to let their lights shine. They are called to serve as living testimony to the Gospel and, thereby, to draw others to the church.