Missionaries preach the Christian faith (and sometimes administer sacraments), and provide humanitarian aid. Christian doctrines (such as the "Doctrine of Love" professed by many missions) permit the provision of aid without requiring religious conversion. However, Christian missionaries have been implicated in the genocide of indigenous peoples.

Missionaries are those sent out or go for the primary purpose of evangelizing largely unreached people groups at “the End of the Earth.” They often place themselves in a window of the world where most have never heard the name of Jesus Christ.

Missionaries spread the Christian message abroad. They do not necessarily preach – instead, they may spread the message through their actions, for example by helping with charity projects. This is how Christianity as it is known today has spread across the globe.