Albert Barnes Commentary Jeremiah 7:21

"Thus saith Jehovah of hosts, the God of Israel: Add your burnt-offerings unto your sacrifices, and eat ye flesh." — Jeremiah 7:21 (ASV)

The meaning is: Increase your sacrifices as you will. Add burnt offerings to peace offerings. All is in vain as long as you neglect the indispensable requirements of obedience and moral purity.

To "eat flesh" is equivalent to sacrifice. The flesh of animals offered in sacrifice was usually eaten by the offerers, and this meal was regarded as a symbol of reconciliation. God and man partook of the same victim and so were made friends.

This passage (Jeremiah 7:21–28) is the Haphtarah (a lesson from the prophets), read after the Parashah (Leviticus 6–8), which is the Lesson from the Law. The selection of such a Haphtarah shows that the Jews thoroughly understood that their sacrifices were not the end of the Law, but a means for spiritual instruction.