God's Character Is Our Defence
Stephen had been accused of saying that Jesus would destroy the temple, and change the customs handed down from Moses. In fact, Jesus was speaking of the temple of His own body which would die (John 2:19-21); and Jesus said that He had not come to abolish the Law and the prophets, but to fulfil them (Matthew 5:17). So the charges put by the false witnesses were clever lies, false but based on enough truth to make them believable.
However, Stephen did not even attempt to defend himself by arguing about the charges. This trial was not about him; it was all about Jesus. He knew his job was to proclaim Jesus Christ as Lord and call the council to repentance. His method, inspired by the Holy Spirit, was to remind his audience of religious leaders of how God's character was seen in the history of God's people.
He started with Abraham who heard God calling him to leave what was familiar, trusting Him to fulfil His promises. Although the religious leaders were fixed on the physical land of Israel, God's first promise to Abraham was to establish his descendants as a model of all who would respond in faith and love to God (Genesis 12:2-3). Fulfilment of that promise depended on having a son… but Abraham and Sarah were childless. Abraham trusted God's Word and character, and on the strength of that conviction moved out of Ur (in what is now Iraq) to Haran (in what is now SE Turkey).
Human nature longs to be settled in a place, a home, a country. But God is longing to add people to His kingdom who are primarily secure in His promises and not a physical place or structure (Hebrews 11:8-10). He wants us to be flexible, mobile and trusting so that we can work with Him to fulfil His purpose and not just to defend our own interests. But if we have no confidence in His character, we will not trust His Word and therefore seek to carve out our own lives to suit ourselves. Follow Stephen's example when you sense the need to defend yourself. Talk about your amazing Saviour and what He has done, and let the Holy Spirit convict hearts who will listen.