From The Life and Times of Bruce Gerencser:
And he said unto them, Go ye into all the world, and preach the gospel to every creature. He that believeth and is baptized shall be saved; but he that believeth not shall be damned. (Mark 16:15,16)
Those of us raised in Christianity recognize these verses as the “Great Commission,” the charge to go forth and spread the message of Christianity to the rest of the world. As the only Christian religion in the western world for nearly 1500 years, the Catholic church took this message seriously. Since the Edict of Milan in 313 CE decriminalizing Christianity and gaining Emperor Constantine’s patronage, and later the Edict of Thessalonica of 380 CE making Christianity the state religion of the Roman Empire, the Catholic church was intertwined with government for centuries. Spreading a religion is quite easy when supported by the government.
Some Evangelical Christians have taken the Great Commission seriously as well, raising large sums of money to support missionaries to proselytize the “lost” throughout the world. Sometimes the “lost” include Catholics, who are not considered “True Christians” by many Evangelical sects. Anyone who is not part of “True Christianity” is considered “lost” and thus ripe for evangelizing. Evangelical Christians are also exhorted by their pastors to proselytize to their neighbors, friends, and coworkers. Where I grew up in the Bible Belt, most of the people I knew were more or less the “right” type of Christians — Southern Baptists as we were, a variety of other types of Baptists, Church of Christ, Methodists, Church of the Nazarene, etc.