The term 'believed in Jesus' has deep implications [not solely interpreted], since Jesus is only the son and intermediary, it has to encompass the imperative faith and belief in God, thus surrendering of one's will to God, entered into a contract with God and to comply with every word of God [via Jesus] to one best ability.
Then explain why Jesus said the criminal dying next to him on the cross would join him in heaven? He didn't fulfil the strict requirements of what you claim to be a QED argument. All he did was to believe/have faith - and he was saved. From my perspective, the BIble is not consistent enough to make an argument that defines a Christian conclusively.
Re “saved/enter heaven" upon believing in Jesus is only with reference to something like be given a passport or visa to another country but there is no guarantee one can enter the country automatically without being subject to the respective immigration processes and authority. If the immigration authorities discover any new knowledge the person has not comply to its laws s/he may be deported instantly.
I don't believe this analogy reflects the New Covenant. Where did you get this idea of Christianity from?
A person can sincerely and easily declare his belief in Jesus Christ, but subsequently be overwhelmed by his selfish desires and commit the greatest sin and many critical sins later. Example, the pastors who were caught as pedophile, adulterers, rapists, killers, etc. Are they saved/will-enter-heaven just because in their earlier years and are acknowledged by the congregation that s/he has believed in Jesus?
I think that sincerity is the hallmark of Christianity, obviously too. It is propounded by pastors (rightly or wrongly) that if a person sincerely believes in Jesus, the desire to sin will disappear. I don't believe that people who commit the sins you mention will “enter heaven”, but if they repent and sincerely believe in him, their sins will be forgiven. The entire thrust of the NT is faith, not laws or rules like the OT, so I'm not inclined to argue that obeying a set a strict of rules is the mark of a Christian or defines one. From my perspective, Christianity is a state of being, rather than strict accordance to doctrine.
One thing we can infer with certainty is, in principle, these sinners had already broken their covenant and contract with God upon their committing the serious sins.
I have heard pastors propound the opposite – that sin does not break the New Covenant, since it is founded on the principles of love and forgiveness, not law and punishment.
Note
Matthew 19:24 "I'll say it again-it is easier for a camel to go through the eye of a needle than for a rich person to enter the Kingdom of God!"
Thus there is still a lot of work to be done by a 'Christian' after the initial believing in Jesus, surrender one's will to God, and complying with God's words to qualify one for a passage to heaven with eternal life.
Hmm, the meaning of that statement is clear, yet you've interpreted something which strikes me as being quite far from what it actually means or intended. It seems as though you're inferring your claimed QED conclusion from every source you quote. How many meanings do you think that statement has, just the one that confirms what you believe?
That is hand waving about nothing.
You can tell me where I am wrong and where I agree, I will take steps to correct it. I have been doing that with feedback from others over the years.
I think its a bit more than that, but subtlety is seemingly lost with you. Considering the nature of our discussions, why would I get into a debate with you about where I think you are philosophically/epistemologically right or wrong? The thing is, you claim to be open to discussion about this, but the outcome is so predictable I wouldn't bother. Also, I'm not qualified in philosophy, so it isn't really my place to tackle you on those grounds, but I think as we discuss/debate my points of view will come to the surface, so it will be apparent where I think you're wrong.