You pose an interesting question. If someone believes Jesus was a great prophet but not the Son of God, are they Christian?
Of COURSE you guys 'really believe'!
WHO ever said you didn't??
Like I told my wife, the last time she got us lost in the woods while I was driving; "Well I believed that the last turn I made was right."
Because otherwise wolves in sheeps' clothing will lead people astray. That is what Paul fought against.
Please explain to me how men, without God's assistance settle these disputes.
Of course we need God to be in control. It is the internal witness of the Holy Spirit that equips believers to fight against heresies.
Last question is someone who believes in Jesus, but has a diff rent understanding than you do "passing themselves off" or do they really believe?
They believe in something that is false - that does not come from God. Not everyone who says "Lord, Lord" will go to heaven.
(This coming from somebody who belongs to an organization where the stress is on men's revelations? ... from an organization where the stress is that 100% of everything God does is revealed to prophets? ... Based upon a literal, wooden interpretation of Amos 3:7: Surely the Lord GOD will do nothing, but he revealeth his secret unto his servants the prophets.)
Last question is someone who believes in Jesus, but has a diff rent understanding than you do "passing themselves off" or do they really believe?
Believing in the "wrong" Jesus is no light matter. The apostle Paul asked the Corinthians: Suppose someone comes to you and preaches about a Jesus different from the Jesus we preached about? (2 Cor. 11:4)
Likewise Jesus made it clear that it wasn't simply just knowing any old god. He prayed to His Father: "And THIS is eternal life -- that you KNOW the ONLY TRUE GOD, and Jesus Christ whom He has sent." (John 17:3)