What Does it Mean to be A Christian?

There are many people who categorize there faith into either Catholic, Protestant, Methodist, Lutheran, Baptist, Orthodox, and many more denominations. My question to you is no matter what denomination you are there are certain guidelines to being a faithful Christian and why do we differentiate between religious beliefs? Don't we all have a common goal to worship the Lord who gave us this life we are so fortunate to have. I guess what I'm trying to ask is although there are so many differences in religion practices, why are these here and is there a common ground we can all agree on what it means to be a Christian?