But how do you know what the actual message of Christ is, without the Bible?
Most of the early believers did not have bibles, nor could they read.
The earliest believers in Jesus were Jews and heir Bible was the Tanak, they were almost all literate as that was a priority with Jewish people to read and understand scripture.It is simply not true that they were illiterate, and wherever the gospel has gone throughout the pagan world, so also has literacy!