17 Then the Lord spoke to Moses, saying, 18 “Speak to Aaron and to his sons and to all the sons of Israel and say to them, ‘Any man of the house of Israel or of the aliens in Israel who presents his offering, whether it is any of their [o]votive or any of their freewill offerings, which they present to the Lord for a burnt offering— 19 for you to be accepted—it must be a male without defect from the cattle, the sheep, or the goats. 20 Whatever has a defect, you shall not offer, for it will not be accepted for you. 21 When a man offers a sacrifice of peace offerings to the Lord to [p]fulfill a special vow or for a freewill offering, of the herd or of the flock, it must be perfect to be accepted; there shall be no defect in it. 22 Those that are blind or fractured or maimed or having a running sore or eczema or scabs, you shall not offer to the Lord, nor make of them an offering by fire on the altar to the Lord. 23 In respect to an ox or a lamb which has an [q]overgrown or stunted member, you may present it for a freewill offering, but for a vow it will not be accepted. 24 Also anything with its testicles bruised or crushed or torn or cut, you shall not offer to the Lord, or [r]sacrifice in your land, 25 nor shall you accept any such from the hand of a foreigner for offering as the [s]food of your God; for their corruption is in them, they have a defect, they shall not be accepted for you.’”
26 Then the Lord spoke to Moses, saying, 27 “When an ox or a sheep or a goat is born, it shall [t]remain seven days [u]with its mother, and from the eighth day on it shall be accepted as a sacrifice of an offering by fire to the Lord. 28 But, whether it is an ox or a sheep, you shall not kill both it and its young in one day. 29 When you sacrifice a sacrifice of thanksgiving to the Lord, you shall sacrifice it so that you may be accepted. 30 It shall be eaten on the same day, you shall leave none of it until morning; I am the Lord. 31 So you shall keep My commandments, and do them; I am the Lord.
32 “You shall not profane My holy name, but I will be sanctified among the sons of Israel; I am the Lord who sanctifies you, 33 who brought you out from the land of Egypt, to be your God; I am the Lord.”
God doesn’t want sacrifices that cost us nothing, and he doesn’t desire our junk. However, there were other reasons for some of these rules about sacrifices, and likely the most important was that a sacrifice was food for the priests. If you bring a sick animal to feed the priests, that puts the priest at risk. And with medical care being what it was back then, that could even result in death.
Again, God wanted the Israelites to honor the priests, and He wanted them to bring their best. Not an animal who was already on death’s door, or that was inferior because it couldn’t breed, or that would sell for less at the market because it was deformed. He doesn’t want our second-rate offerings either, God asks for our best every day.