Many people will say that Christianity is belief in the teachings of Jesus; but somewhere along the line they never get back to that.  It changes to everything from talk about his miracles to talk about a "personal relationship with him".  

I am going to start with a short list of what Christianity is NOT, so that we can get back to the real Foundation of our faith, when we've narrowed the subject down a bit.

    Christianity is not about Jesus' miracles.  Most professing Christian believe Jesus did miracles... lots of them.  But he is also recorded as having said that evil people are the ones who go looking for miracles.  Besides, it's pretty hard to convince anyone today about stuff they can't see happening right now, and I personally have never found the Pentecostal emphasis on miracles to be very convincing either (though I do accept that sometimes people experience things that are genuinely miraculous).

    It's not about "churches" (i.e. religious organisations).  The supposed two billion people who call themselves Christians on census forms really mean nothing if they're not following the teachings of Jesus, and my experience is that you'd probably have to discard about a million to find just one who is doing that these days.  Besides, as soon as you get into organisations, you find yourself up to your neck in wars, political in-fighting, disgusting materialism, and the like.

    It's not about religious experiences.  There really is no consistency even within denominations that insist they have boiled it down to some specifics (like speaking in tongues or saying the "sinner's prayer").  Religious experience is subjective, and none of the criteria used for sorting out the good guys actually work.

    It's not about theological statements, e.g. that Jesus is the Messiah or the Son of God.  Even his chosen followers only gradually came to believe some of those doctrines, and nothing has really stopped some of the worst characters throughout history from reciting the various creeds.  Jesus said, "Why do you call me Lord, Lord, but refuse to obey the things that I have taught."

    So it finally comes down to HIS TEACHINGS... something we can examine and even experiment with right now, and compare with anything anyone else has ever taught.  Suddenly Jesus stands head and shoulders above all the rest.  But sadly, Christianity as taught by Jesus has largely gone the way of the dinosaur.  Ironically, he predicted that too, saying that, about the time when he is ready to come back to Earth, it will be like it was in Noah's day, when God could only find one family on the entire Planet who was genuinely trying to obey him.  But the teachings are still there, in just about every Bible... if only someone would dare to practice them.  Those teachings are so amazing (at least IMO) that they provide me with all the "religious experience" I will ever need; convincing proof that Jesus really was something pretty out of this world, if not the only begotten Son of God;  and hope for miraculous and supernatural manifestations on a par with living forever, even if I should die on the way.  

    In conclusion, there is some truth in all of the first four things listed above, even though they do not reliably and exclusively define Christianity.  Their main function, however, seems  to be to stop people from even thinking about, much less applying, the true test of a Christian, which is our acceptance of what Jesus taught, and our efforts to apply those teachings in our own lives.  If we would do that, it will lead to religious experiences, occasional miracles, fellowship with others who believe the same, and a greater appreciation for things like the divinity of Jesus.  But, until we get back to the Cornerstone of Jesus’ teachings, all of the other definitions of Christianity will ultimately fall flat and become big disappointments.