The Catechism in Questions & Answers

98. What does the term “Lamb of God” mean here?

The designation “Lamb” is intended to introduce Jesus as the Redeemer, and is reminiscent of Isaiah 53: 7: “He was oppressed and He was afflicted, yet He opened not His mouth; He was led as a lamb to the slaughter.” Since ancient times, lambs were considered the sacrificial animals of preference in the Old Testament. The image of the slaughtered “Lamb of God” is a reference to the sacrificial death of Jesus Christ.