India at the time of the Buddha had a plethora of religions and myriads of views. Some religions believed the world is controlled and ruled by Brahma, one of the celestial beings. If Brahma is happy, we’ll all be saved; if not, we’ll go to hell. In order to worship Brahma, people killed all sorts of animals as offering to him. This is ignorance.

~Depicted from THE HANDBOOK FOR LIFE'S JOURNEY - On The Three Poisons-How to Refute Ignorance