Why did God give rules for sacrifice?

God gave rules to show how to 
worship Him and be forgiven for sin.

The book of Leviticus contains many rules for the Israelites, but we do not obey all the rules in Leviticus today because we trust Jesus, who obeyed the law perfectly for us. The Israelites had to make a blood sacrifice for their sin every year. Jesus sacrificed His blood on the cross to pay for our sin once and for all. (Hebrews 7:26-27) When we trust in Christ, God forgives us of our sin.