The mission Christ gave us as the Church is to reach the world for him.
John 3:16 says "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life."
We want to reach our world with the Gospel and one way we do this is by supporting Missionaries. These Missionaries go in our place where we cannot go.
They are our representatives in countries all around the world!