sounds a lot like a religion, how do you define religion?
The letters you speak of (penned by apostles of Jesus) are exactly as you describe. They were humans, trying to do what a divine being told them to do. It appears they went about it(at least partially) by writing letters. The passage I believe you are referring to, where Jesus instructs his disciples is:
> Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,
This doesn't say to "spread religion", it literally tells them to teach and baptize all nations. They went and wrote letters, and here we are thousands of years later calling that "religion".
What is important to you? I see this conversation as attempting to make disciples of all nation. If it's successful for anyone(not you necessarily, maybe someone reading)...then hoo-ah! That's a win! If not, the instructions that preceded the passage you refer to say that I should "shake the dust from my feet", and leave the metaphorical house(s) that will not listen.
I don't know how we got from 0-50 A.D. to where we are now, regarding "religion", but I don't see even the most remote connection from the behavior of Jesus' disciples and their letter writing, to whatever the heck is going on in modern day.