In the days of the Buddha, it was common for people to kill animals as a sacrifice, or offering to their gods. This was intended to make the gods pleased and willing to reward those who made the sacrifices with answers to their prayers.
The Buddha saw that this custom was cruel and mistaken. Even as a young
boy (and boys are often cruel to animals and insects), he had tried to protect
animals from suffering. He not only wished to save the sheep and cows and other animals from the suffering of being sacrificed, but he wished to protect the people who wanted to kill these poor animals from the suffering that would follow their acts.
He knew that those who sacrificed animals were actually creating the cause
for their own future suffering. The Buddha taught:
”It is not right to make another unhappy so that you can be happy. Everyone wants to remain alive just as you do. Therefore, if you sacrifice an animal, you are just being selfish. And I have said again and again that a selfish person finds nothing but unhappiness in life."
Many of the people who heard these words realized that they were true. Immediately they gave up their custom of sacrificing animals. In this way a great deal of unhappiness was brought to an end and the Buddha had taken a big step towards achieving his life mission of lessening the sufferings of both humans and animals.