First, to be clear, those not born again are not Christians. Those of the Spirit? Yes, according to the Bible teaching that the Holy Spirit leads into all truth, and testifying that it's my experience that all those I've known who are of the Spirit, those of nothing but truth, believe all basic doctrines the Bible teaches. There are difficult eschatological matters we seek a most plausible Bible accounting for, but you'll readily find any true scholar admit that their view is their view, and why, and these not basic doctrines, like eternal security, the deity of the Lord Jesus, etc.
Contrary to what some people say about divisions, yes, there are a lot of divisions, Christians versus also-ran fabrications, religions and doctrines of men and demons (who also scratch each others' eyes out), but I've been awed how there is an entire community of agreement on all the major issues, who also see the unity and harmony of the entire Bible. I seldom say anything, but anytime I've been accused of being confused or such, irony is that I'm not at all confused, at perfect peace with everything the Lord and His servants, my betters, have faithfully taught me, neither have once seen a scintilla of reason to turn from truths that are even violently protested by evil men, only showing that where there's smoke, there's fire, of a truth the lady doth protest too much. You could say that, so very simply, a Christian understands the Bible, and believes the Bible, thanks and glory to the Spirit of Christ, and one verse never actually contradicts another.
Almighty God is quite certain, clear and consistent, altogether perfect. You have to look to man to muck something like this up.