How do you know which is which? I'm asking honestly.
The stuff from Leviticus (the Old Testament, which is most of the screed) is old Mosaic Law.
Christianity, while sharing origins from the Old Testament, is based on doctrines established in the New Testament, which supercedes the old law. For instance, Christ is the sacrifice-- no animals are needed in Christianity due to his sacrifice. And the aspects of forgiveness established by Christ overshadow the killing of unbelievers, etc.