If it were up to you to answer from your gut: "Which issues are important enough to exclude people from heaven over?", what sort of issues would you come up with? If you interview people in your church and asked, "On what grounds should people be excluded from salvaton and fellowship?," what sorts of answers would you expect to hear?
Genocide? Exploitation of children? Drug use? Maybe someone might say "no grounds at all."
How would you respond or those people respond to suggested issues like: "Should people be barred from heaven because they failed to believe in Jesus?" "Should people be barred from heaven who did believe in Jesus but failed to have the right particular beliefs about His divine/human identity?" "What about people's beliefs about resurrection?" "What about people's beliefs about how the Jewish law is related to Christianity?"
Do these seem like foolish, trivial matters that no one should be barred from heaven over? Do these seem like petty arguments over nothing? If so, consider that Peter, Paul, and John were willing to draw lines over these matters.
Peter said people must find salvation solely in Christ (Acts 4:12).
Paul said the Galatians risked losing God's grace over their acceptance of a Judaized gospel (Gal 5:4). Paul also called out by name those who taught falsely about the resurrection and said "the Lord knows who are His," implying that these people weren't (2Tim 2:16ff).
John wrote a great deal of his gospel and epistles to sort out false beliefs about Christology. Particular John combatted the early seeds of Gnosticism that plagued the church for the first couple of centuries. John picked up his pen and took the time to warn people about those who disagreed about whether Jesus really incarnated as a flesh-and-blood human. These people did believe that they were Christians. These people did believe Jesus really was the right way to heaven. But they didn't believe He was really human like you and i are human. Doesn't it seem like a minor difference? Yet John writes:
"Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. This is how you can recognize the Spirit of God: every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist." (1John 4:1-3) [Does it appear that John would've considered the Council of Nicea a petty, insignificant debate?]
My point is this: Do you take it for granted that what seems like a foolish or insignificant issue to you would also seem that way to Christ and His apostles? Just because something feels like a petty quibble to me, does that make it a petty quibble?
Suppose you were a Jew, an inhabitant of Jerusalem all your life, living in the first century during the earthly ministry of Jesus. For as long as you can remember, there has been animal sales in the temple for people who are offering sacrifices. It's a fixture and you probably haven't questioned it much. Would it really seem to you like something outrageous or egregious? i really can't say for sure that it would seem that way to me. Yet Jesus was willing to throw tables around and scare away people and livestock with a whip and yell about it.
So what issues seem petty to me? What debates seem insignificant or a waste of time to me? Whether people believe Christ is the sole way to heaven? The particular way a person needs to be baptized? The particular way the Lord's Supper needs to be conducted? The particular way worship music is practiced?
But just because any of these issues may appear to me to be foolish and insignificant, does that automatically mean that Christ thinks of them the same way?
How do i know Jesus wouldn't shove over pulpits where people teach that non-Christians are okay as they are? How do i know He wouldn't overturn tables in my auditorium and shout about conducting Communion correctly? How do i know he wouldn't throw song books across the room or knock over amplifiers and drum sets and shout about them? How do i know He wouldn't drain baptistries or knock over water bowls and condemn the way a congregation baptizes? If i can't know for certain that i wouldn't think the money changers in the temple was no big deal if i were a first century Jew, what right do i have to assume i'm correct that these kinds of things are no big deal and Jesus would agree?
i'm not suggesting that there is no way to know at all what does and would matter to Christ and what are important issues. What i'm pointing out is that people (myself included) have a tendency to think that what feels important 'to me' actually is important; and what feels unimportant 'to me' actually is unimportant. Based on that tendency, people can conclude that any matter of religious belief they feel is unimportant, Christ must feel that it's unimportant as well.
But if Jesus drastically challenged the gut-level priority list of some religious people of His own day, then who's to say He wouldn't challenge ours as well? Thus, in the end, i can't assume that it would be petty to bar people from heaven over certain issues just because they seem like petty or unimportant issues to me. If in the end Christ does withhold eternal life from someone over something that i consider trivial, what that demonstrates is that my values are backwards, not Christ's.