Unashamed Power
Peter's boldness did not come from arrogance or assertiveness, but from a confident assurance that Jesus Christ is Lord. The religious court accused the apostles of disobeying their ruling 'not to speak about Jesus'. But their reply was the same as the last time they were arrested (Acts 4:19-20):"We must obey God rather than human beings!"
Peter was unashamed about the resurrection of Jesus and His ongoing power. The court had sentenced Him to be crucified but God had raised Jesus from the dead, so that meant that God was on the opposite side to the religious leaders. That was a very serious charge as Peter went on to explain that Jesus is God's Prince of Peace and Saviour. He was sent to bring all of His people to repentance (including their leaders) so that God could forgive their sins. It was a gospel message directed at the court.
The apostles were eye witnesses (2 Peter 1:16); they had met the risen Jesus (John 21:15-19). They had been filled with the Holy Spirit who urged them to tell what they had seen (Luke 24:48-49). Their teaching in the temple was not belligerent defiance of the court but simple obedience to the Lord. But when they had spoken, some of the Council demanded the death penalty for the apostles, just as they had for Jesus (Mark 14:63-64). They were so angry that Jesus was more important than them.
Sin's chief characteristic is to make 'self' more important than God. People become their own gods and deny Jesus' right to be King (Luke 19:14). So they will ignore Him, slander Him and want to dispose of Him and His people. And yet the Holy Spirit brings conviction of sin as God's people speak the truth about Jesus (Acts 2:37). What will they do with the knowledge that they are wrong before God? Either repent or resist. That is true of all your friends and colleagues. God is good in urging them to repent but that is the choice they have to make (Romans 2:4). In the meantime, they may well take their anger out on you. But be encouraged, the Holy Spirit is at work through your words and witness; and some will repent and be saved.