Learning Persuasion

I guess all of this theology talk with the Jehovah's Witnesses is challenging me as to why I believe what I do. Is it just because I want it all to be true? I think perhaps I have been very lazy in not really bothering to look up all the reasons behind it and properly studying the Bible because I'm "sure" that it will be right. I'm genuinely not worried that by looking into it I'll find that it's not true... but I think I should care enough to want to be sure and be able to persuade others on an intellectual level, as Paul did (Acts 17:4, 18:4, 26:28-29, 28:23). As, as I've found when talking with Mormons, the whole "I'm just sure that it is true" isn't very convincing... and if I really want to be loving people and reaching people with the Gospel, then I should be willing to go to the effort of really looking into these things hard and learning why I believe what I do.

The first thing I want to look into with regards to discussions with my Witness friends, is the history of the Trinity. They say that the concept of the Trinity wasn't found in the Old Testament and wasn't an idea the Jews were familiar with, and neither is it mentioned in the New Testament by Paul or Peter or Jesus himself. They say it was a concept introduced about three centuries after Jesus was around, and primarily as a result of Constantine pushing it for political reasons.. but obviously it could be that the sources used in their pamphlet are biased in some way. So I'm going to do some digging... :)