What is the purpose of the commandments ?

The "Seven Commandments" were put in place to provide law and order.

"They (the pigs) explained that by their studies of the past three months the pigs had succeeded in reducing the principles of Animalism to Seven Commandments. These Seven Commandments would now be inscribed on the wall; they would form an unalterable law by which all the animals on Animal Farm must live for ever after."