The Catechism in Questions & Answers

732. What was the significance of sacrifice in the old covenant?

Sacrifice was of great significance in the old covenant. Through their sacrifices, the people sought to express gratitude, turn away the punishment of God, or bring about reconciliation.
Sacrifices were brought in many different forms. The Mosaic Law specifically prescribed all the details of the sacrificial service (cf. Leviticus 1-7).

Old covenant: see explanation of Question 175. Mosaic Law: see Questions 272. et seq.