Why are there denomination in Christianity?

Answer 1

Since the time Jesus was walking around on the Earth, people have had different ideas about what He was saying and what He meant. Jesus told alot of parables (stories with metaphors to life) and He rarely explained what they meant in definitive terms (pretty much because people wouldn't understand Him). So people would go out and teach their understanding of what he meant. As you got further and further down the line, eventually you get people arguing about what He meant. This leads to churches splitting, with those who believe one thing going one way and those who believe another going another way.

Nowadays, you get splits based on huge aspects of faith (Catholic-Protestant difference) and the all-too-common splits based on smaller aspects (should homosexuals be married or not, we want this preacher not that, etc.). People are fickle.

Sadly, it's gotten to the point where there are actually people who are questioning whether God is real at all, or whether the Bible is accurate at all... these churches and denomination types tend to fail pretty quickly because they have no basis in God, the Bible, or their own security of faith.

Answer 2

Because some Christians think the way they believe is correct and the way others believe is not correct. Dogma, traditional differences etc. For example: Protestants vs. Catholics