John Oakes is a person who spends his time studying and making arguments for the Christian belief. He believes in God and wants to convince others to believe in Him too.
He reads many books and studies different ideas so that he can answer people's questions about Christianity. This is called apologetics.
Imagine you were telling your friends about your favorite toy, but they didn't believe it was the best toy out there. You would try to explain to them why it's great and why they should play with it too.
That's what John Oakes does, but instead of talking about toys, he talks about God and Jesus.
He uses his knowledge to answer people's questions about why they should believe in God and Jesus, and also to help those who already believe to understand why they believe what they do.