Perhaps one might think of this as being a rather minor affair, but God shows that He had—and so we must have—respect for the life of an animal. God, in the instructions regarding the regular sacrifices, says not to eat the blood! He says this out of respect for the animal because its life was in its blood. The blood had to be drained on the ground, not imbibed by a human being.
Animals have at least a low level of feeling. They experience fear; situations can frighten them. What animal owner does not think that his pet, his dog or cat, has a special relationship or special feeling for him? Can we extend that out—that a bullock, a goat, a sheep, a kid of the goats, or a lamb might have feelings too? Not human feelings, certainly, but they have life and they symbolize—every single one of them—the life of Jesus Christ. How many animals had to give their lives to make a witness, an example of that? We will never know, but just to help us understand, Josephus records that one year during his lifetime, the Romans took a census of all of the lambs that were killed in Jerusalem, and 256,000 lambs were killed on Passover alone—256,000 lambs on one Passover just to teach a lesson to Israel and to us.
Perhaps it would help us to understand why God told the Israelites in Exodus 12 that keeping Passover was to be a family affair. It was not done at the Temple or the Tabernacle. God commanded that everybody killed his own lamb—every family. He wanted to make the point to all that each person is responsible for the death of the Lamb of God, Jesus Christ!
Consider that Israelite families were not rich. Most of them had small herds and flocks—just a few sheep and lambs. They lived, in most cases, with their animals, and when they put a lamb to death on Passover, it was very likely the family pet! They killed and ate something that was very close to them—something that they had treated like part of the family. This was an object lesson, and God allowed millions of them to occur!
As far as God is concerned, nothing is too great a price to pay for us.