3:16. And the priest shall burn them upon the altar, for the food of the fire, and of a most sweet savour. All the fat shall be the Lord's.

3:17. By a perpetual law for your generations, and in all your habitations: neither blood nor fat shall you eat at all.

Fat… It is meant of the fat, which by the prescription of the law was to be offered on God's altar; not of the fat of meat, such as we commonly eat.

Leviticus Chapter 4

Of offerings for sins of ignorance.

4:1. And the Lord spoke to Moses, saying:

4:2. Say to the children of Israel: The soul that sinneth through ignorance, and doth any thing concerning any of the commandments of the Lord, which he commanded not to be done:

Ignorance… To be ignorant of what we are bound to know is sinful; and for such culpable ignorance, these sacrifices, prescribed in this and the following chapter, were appointed.

4:3. If the priest that is anointed shall sin, making the people to offend, he shall offer to the Lord for his sin a calf without blemish.

4:4. And he shall bring it to the door of the testimony before the Lord: and shall put his hand upon the head thereof, and shall sacrifice it to the Lord.