The lesson that I take from this book is largely a political one: Authority is easily abused.
Corruption, however, is not automatic. It's gradual and that is a life lesson, I think. Napoleon and Snowball both began to take advantage of their position early on, but it took quite a bit of time before Napoleon began to wear human clothes and walk on two feet.
There was time to stop him. Action could have been taken. One moment of inaction, however, led to another as the animals of the farm chose to turn a blind eye to what was actually happening. Perhaps this suggests another comment on life and people: We see only what we want to see.