The Apostles John and Paul were zealots. The both believed Jesus would return before either of them died. In addition, they added their own teaching because they wanted things their way.
Then came the Roman Catholic Church which invented all sort of doctrine that Jesus never taught or is even Biblical. Heaven. Hell. Immortal souls. What books will be in the Bible. What books won't (Whatever happened to "all scripture is inspired"?)
The fecal matter really hit the oscillating blades in 1517AD with Martin Luther telling everyone "once saved, always saved" and "just read the Bible with your own understanding and that is all you need." Now we have over 40,000 denominations of Christianity thanks to Luther.
Jesus only taught this -
- Love everyone as you would love yourself
- Judge no one
- Chose forgiveness over justice
- Take care of widows and orphans
- Feed the hungry
- Heal the sick
- Be content with the necessities of life
- Live in the moment and don't worry about tomorrow
As one professor wrote in his book "What Did Jesus Really Say - How Christianity Went Astray" - Read Matthew, Mark, and Luke. That is all Jesus taught.