Why isn't there just one and only one denomination of Christianity?

Read the Bible and you will never find it claiming that truth has been in the majority at any time in human history. People are experts at taking something that is good and twisting it to serve our own selfish means. The Bible is an influential book, and something that widespread and important is ultimately going to get into many of the wrong hands as well as the right hands. That is why we as individuals need to study and understand it so that we can identify truth and lies.