The role of Jesus' disciples and followers on earth is described in this verse. Jesus compared His disciples to salt in the previous verse (Matthew 5:13) and referred to them as the light of the world in this verse. On top of this metaphor, Jesus adds another one by describing a city built on top of a hill. A city cannot be hidden. Even in the darkness of night, the city can be seen and found.
Our role as Christians is to live not just in this world but also above it so that all can see God's glory through the light of the world. As Christians, all that we do and all that we are should reflect the glory of the Lord Jesus Christ with a purpose so that through our lives, the heavenly Father will be glorified. 
We should seek to live a life filled with good works in the power of the Holy Spirit. Each of us has a holy responsibility to serve others, to forgive one another, and to reflect the beautiful character of Jesus in all that we do and say because we are the body of Christ, and we will shine the light of Christ into the world.

Dear Heavenly Father, it is You, the True Light of the world, who gives life and love to all those who believe in You. It is You who builds the city that cannot be hidden. I pray that the light of Christ will illuminate the dark world. Please let me be entrusted in the corner of the world where You have placed me to bring the light, the life, and the love of Christ to those who are in pain. Never let me forget that without Your Grace, I can do nothing. With the Holy Spirit, I will act as Your body for those in need. 
In Jesus's name I pray. Amen.