Atheists who become Christians

[Alex K]

I can't understand how an atheist who has researched the arguments is able to believe in Christianity.

I think you've at least partly answered your question. We often say about fundamentalists that it may not be possible to reason someone out of a position they haven't reasoned themselves into in the first place. The same is probably true in reverse - I'm sure there are atheists who haven't thought deeply about the issue and simply were atheist by default because of their upbringing, or simply contrarian. I can imagine how someone like that would become theist.