Actually, some sins just make you unclean until you sacrifice some animals, such as wet dreams, menstruation, and childbirth.
Leviticus 15:16-33 (New International Version)
16 " 'When a man has an emission of sperm, he must bathe his whole body with water, and he will be unclean till evening. 17 Any clothing or leather that has sperm on it must be washed with water, and it will be unclean till evening. 18 When a man lies with a woman and there is an emission of sperm, both must bathe with water, and they will be unclean till evening.
19 " 'When a woman has her regular flow of blood, the impurity of her monthly period will last seven days, and anyone who touches her will be unclean till evening.
20 " 'Anything she lies on during her period will be unclean, and anything she sits on will be unclean. 21 Whoever touches her bed must wash his clothes and bathe with water, and he will be unclean till evening. 22 Whoever touches anything she sits on must wash his clothes and bathe with water, and he will be unclean till evening. 23 Whether it is the bed or anything she was sitting on, when anyone touches it, he will be unclean till evening.
24 " 'If a man lies with her and her monthly flow touches him, he will be unclean for seven days; any bed he lies on will be unclean.
25 " 'When a woman has a discharge of blood for many days at a time other than her monthly period or has a discharge that continues beyond her period, she will be unclean as long as she has the discharge, just as in the days of her period. 26 Any bed she lies on while her discharge continues will be unclean, as is her bed during her monthly period, and anything she sits on will be unclean, as during her period. 27 Whoever touches them will be unclean; he must wash his clothes and bathe with water, and he will be unclean till evening.
28 " 'When she is cleansed from her discharge, she must count off seven days, and after that she will be ceremonially clean. 29 On the eighth day she must take two doves or two young pigeons and bring them to the priest at the entrance to the Tent of Meeting. 30 The priest is to sacrifice one for a sin offering and the other for a burnt offering. In this way he will make atonement for her before the LORD for the uncleanness of her discharge.
31 " 'You must keep the Israelites separate from things that make them unclean, so they will not die in their uncleanness for defiling my dwelling place, [
a] which is among them.' "
32 These are the regulations for a man with a discharge, for anyone made unclean by an emission of sperm, 33 for a woman in her monthly period, for a man or a woman with a discharge, and for a man who lies with a woman who is ceremonially unclean.
Deuteronomy 23:10-11 (New International Version)
10 If one of your men is unclean because of a nocturnal emission, he is to go outside the camp and stay there. 11 But as evening approaches he is to wash himself, and at sunset he may return to the camp.
Leviticus 12
Purification After Childbirth
1 The LORD said to Moses, 2 "Say to the Israelites: 'A woman who becomes pregnant and gives birth to a son will be ceremonially unclean for seven days, just as she is unclean during her monthly period. 3 On the eighth day the boy is to be circumcised. 4 Then the woman must wait thirty-three days to be purified from her bleeding. She must not touch anything sacred or go to the sanctuary until the days of her purification are over. 5 If she gives birth to a daughter, for two weeks the woman will be unclean, as during her period. Then she must wait sixty-six days to be purified from her bleeding. 6 " 'When the days of her purification for a son or daughter are over, she is to bring to the priest at the entrance to the Tent of Meeting a year-old lamb for a burnt offering and a young pigeon or a dove for a sin offering. 7 He shall offer them before the LORD to make atonement for her, and then she will be ceremonially clean from her flow of blood.
" 'These are the regulations for the woman who gives birth to a boy or a girl. 8 If she cannot afford a lamb, she is to bring two doves or two young pigeons, one for a burnt offering and the other for a sin offering. In this way the priest will make atonement for her, and she will be clean.' "