1) What is the mainstream Christian view of why Jesus came to earth and why he had to die?
To atone for the sins not only of Adam but also for the personal sins of all human beings. This atonement is received by faith alone or it is not received at all.
2) What was Adam's motivation to rebel? The CO says that Christianity teaches that he wanted to go to heaven and the only way he could do this was to sin and die. Obviously this makes no sense and I sat there thinking there's no way this could be true.
Your instincts are right. Adam's sin had nothing to do with heaven. Adam wanted to run his own life independent of God.
3) I think his point about the deity of Christ is that if he were god (or divine which I understand is different - ie same nature as the Father but not the Father), then the sacrifice would have been too much. I really can't see why that would matter but he apparently thinks its a big deal. He never directly said why he believed this to be the case as if it was so clear that no explaination was necessary.
This CO doesn't understand how sinful sin really is. Jesus had to atone not only for the sins of Adam but for the sins of the whole whole. Accordingly, He had to be more than just the perfect counterpart to Adam.
BTW, the Trinity doctrine does NOT state that Jesus is the Father. It states that the Father and the Son and the Holy Spirit are three distinct persons who together constitute the one true God, Jehovah. In order words, within the nature of the one true God, Jehovah, there are three distinct persons -- Father, Son, and Holy Spirit. The Father is not the Son. The Son is not the Holy Spirit. The Holy Spirit is not the Father. That is the Trinity doctrine.
He also said that Christians don't commerate his death only his resurrection. I looked at my wife and said "what about Good Friday"? Isn't that the holiest day on the Christian calander? " No doubt that the Easter celebration has incorporated "pagan" influences but understanding how that came about makes sense to me that it would. And, to a person that never celebrated Easter, it seems to me that Easter would be a happy time to celebrate the resurrection (that God made good on his promise) as opposed to a more reflective, somber rememberance that Good Friday would involve (I guess, I've never been to a service so I could be way off base).
You are correct regarding Good Friday. Communion (which many Christians observe far more often than once a year) commemorates the sacrificial death -- the blood and body of Christ. In fact, Christians actually PARTAKE of the bread and wine.
Christians celebrate the sacrificial death of Christ since it is the only atonement for our sins.
We also celebrate the resurrection of Christ since it is His triumph over the grave and guarantees the resurrection of all who trust in Him for their salvation.
This CO, like many, is a skilled speaker and everyone was eating up what he was saying. I believe his arguments to be either disingenuous or outright lies when representing what other faiths teach. However, I didn't want my bias towards thinking everything out of a WT speakers mouth to be dishonest to cloud my judgement.
I don't know which it is -- ignorance or dishonesty -- but the CO is completely wrong as stated above. Getting one's understanding of Catholic or Protestant doctrine from this WT CO is like getting one's understanding of WT doctrine from a badly misinformed or biased Catholic priest or Protestant pastor.
If anyone would like to discuss any of this via PM I would be happy to do so.