"Therefore go, and make disciples of all nations, baptizing them in the name of the Father, of the Son, and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you, until the very end of the age."
"How, then, can they call on the one they have not believed in? And how can they believe in the one of whom they have not heard? And how can they hear without someone preaching to them? And how can anyone preach unless they are sent? As it is written: 'How beautiful are the feet of those who bring good news!'"
There are those who believe there are many routes to heaven. We only know of one. That is why we support missionary efforts around the world.