In Leviticus 16 we learn about the Day of Atonement. This chapter could be referred to as the heart of the book of Leviticus. And, since Leviticus represents the heart of the Pentateuch, our passage today represents the heart of the heart of the Law!
Leviticus 4 deals with the sin offering. This was the offering that faithful Israelites offered when they had realized they had committed sin. They realized what they had done, felt the guilt and then brought an offering to atone for it.