What happened to Peter when Jesus was arrested?
When Jesus was arrested, Peter collapsed; his bravado vanished. He cursed, denied ever knowing Him, and ran away in fear, as did the other disciples. Later, after the resurrection, Peter was afraid of no one because he had witnessed resurrection power.
The teaching explains that at Christ's arrest Peter collapsed; his whole facade simply melted away. He cursed, denied that he ever knew Jesus, and ran scared, and the others did too. After the resurrection, however, Peter was afraid of nobody—not Rome, not the Jews—because he had witnessed the power of resurrection. That resurrection power is the bedrock of the Gospel, not merely believing Jesus was a good man or that He died by crucifixion.