What is the purpose of endorsing a check?

I actually had to go to the bank today and so I decided to ask.

The answer I was given is that a check is a legal document (a promise to pay). In order to get your money from the bank, you need to sign the check over to them. By endorsing the check you are attesting to the fact that you have transferred said document to them and they can draw on that account.

http://money.stackexchange.com/questions/3667/what-is-the-purpose-of-endorsing-a-check