1 Cor 1:18-25 and 2 Cor 4:3-6
The cross was a stumbling block and folly to people who considered the kingship of Jesus. It was used to discredit the claims of Jesus - how could a king die and still be king? Where is the power? Where is the light? Foolishness. But what the early church found was the cross, though foolishness to the world, was the fulfillment of everything they had been searching for. And in the face of Jesus, through the resurrection, they saw the light of the knowledge of the glory of God on magnificent display.