The Catechism in Questions & Answers

182. What does the cross signify?

The cross of Christ is a sign that God has reconciled sinful mankind to Himself. In the ancient world, crucifixion was an expression of defeat: a shameful end for a despised person who had been cast out of human society. In the case of Jesus, however, this apparent defeat is a victory: through His death on the cross, He has achieved a work of salvation beyond compare.

“For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God.”
1 Corinthians 1: 18