Something sent by G-d, or maybe just other people, to annoy the s*** out of humans and make their lives miserable. Religion is one of the main tools of seperating people. It is also the main cause of war and hate. Still, it's said to be love. There are many different types of religions and even within those religions there are different groups. For example, there are some people who interpret their religion to mean "Stay out of things" while others believe their religion means "Blow up a country, kill innocent people and serve your G-d!"
I doubt G-d's plan for religion was meant to be like this.
I wish religion never existed because when I think about it, my head hurts horribly.