I am glad to hear that you are settled in and that everything is well. It is also a relief to hear that you and your roommate seem to be getting along and I hope that your friendship with Nathan will grow.
I have thought about your questions and decided on some ways to help you explain, and help Nathan interpret and understand Christianity. In my life I have experienced the same situation you mentioned about Christian terminology and what it means to be a Christian. I grew up in a Christian home under Christian principles and it had not occurred to me “why do I believe in Christianity”? Of course this did not occur to me until I was older and had thought about it for some time. I thought about this world and how it could have been created not by mere chance but by something or someone far more intelligent than mere humans, not by chance. This universe and everything in it was created with superior intelligence and for a purpose. I looked into Christianity and saw how God created the earth; a being far above humans because we were made by him; a perfect powerful all knowing being who created us in his likeness to serve a distinct purpose in this world, rather than leaving it up to mere chance. I knew there had to be a reason for this world and a good one! I looked farther into Christianity and the story of how God created the earth called the Gospel.
I am sure you have heard of the Gospel and read the story, but you must take into account many things before you explain it to a non-Christian. Many non-Christians are not familiar with Christian terminology because they have not looked into Christianity and read the Bible to understand our belief, and we as Christ’s followers must explain the Gospel in a simplified way for people who are not familiar with certain Christian terminology so they can understand the concept and become more familiar with the terminology. One way you can simplify the meaning of these words is to define them and simplify