Because Yahweh is holy, he can only be approached in a certain way. This could only happen on a specific day, by a specific person, and only after they offered the proper sacrifice to make themselves clean. (See: [[rc://en/tw/dict/bible/kt/holy]] and [[rc://en/tw/dict/bible/kt/clean]])
This chapter gives rules for what the high priest had to do on the Day of Atonement. This was the most important day in Judaism. This is when he interceded for the sins of the people of Israel. (See: [[rc://en/tw/dict/bible/kt/highpriest]] and [[rc://en/tw/dict/bible/kt/atonement]] and [[rc://en/tw/dict/bible/kt/sin]])