David_Jay,
I like your response that "belief" does not equate with "mental assent" but that it involves a total change in a person's life and outlook.
I would like to add that the community that wrote John's Gospel focused on the incarnation, the revealing of God's nature through the person Jesus. The Gospel starts off with a cosmic "bang", a revealing of God through his Word, personified in Jesus. In the Gospel all action related to salvation is driven by and originates with God. Man can accept or reject, and those who accept change their lives - they now respond ("believe") and they are now already in receipt of eternal life.
For this reason, the focus in John and the Epistles is with the life of Jesus, not with the death or resurrection. There is no ceremony related to Jesus' death in John (either baptism or "memorial meal") as it is with Paul. His focus lay with the death and resurrection, so he had the cultic ceremonies that related to Jesus' death and resurrection.
I sometimes wonder whether Paul HAD to vociferously state that there was no other Gospel than the one he was preaching because of communities such as the Johannines, who were not concerned with Jesus' death in terms of salvation.
My draft thoughts on John are at:
http://www.jwstudies.com/The_experiences_and_writings_of_the_Johannine_Community.pdf
Doug
PS. I am in no way saying that I agree with either Paul or John. I am simply providng my analysis of what they were telling their local communities.