I've posted about this before, but I love the discussion provoked by my list of 'essential' Christian doctrines. This time, I want to look at it from the vantage point of who is excluded by each essential element. I'll take you step by step through the verses I use to determine the essentials:
Anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.
To be considered a Christian one must:
1. Believe that God exists
2. Believe that God desires relationship
The first, obviously, excludes practicing atheists. The second excludes, at least, the extreme forms of deism (the level of God's direct involvement in the cosmos is, of course, a different discussion that extreme deism which rejects active involvement completely, so far as I understand).
1 John 4:2
Every spirit that acknowledges that Jesus Christ has come in the flesh is from God
To be considered a Christian one MUST:
3. Believe that Jesus came in the flesh
This would seem to exclude some forms of gnosticism and/or some eastern religions that hold to a doctrine of the physical realm being either wicked or imagined.
If you do not believe that I am the one I claim to be, you will indeed die in your sins.
4. Believe Jesus is who He claimed to be
a. Jesus claimed to be the Messiah
b. Jesus claimed to be the Son of God
c. Jesus claimed to be the Lord
* consider further 'I AM' passages
This certainly excludes practicing Jews, not to mention any who claim that Jesus was simply another prophet or 'good moral teacher.'
[If you] believe in your heart that God raised him from the dead, you will be saved
5. Believe Jesus rose from the dead
This would exclude practicing Muslims and, again, Jews. It would also exclude many 'liberal Christians' who reject the historicity of the resurrection.
With this list, I feel we have the proper exclusivity while refraining from division over secondary issues. Given these 5 criteria, we can delay dividing with JW's or Mormons until we actually find out what they, as individuals believe. After all, in the end, people aren't saved by being in the correct group, but by seeking the true God.