The audience heard the truth that Jesus - whom they had killed - was without a doubt both Lord and Christ (Messiah), and this "cut/pierced them to the heart". For many in the audience that day, they were humbled. They understood their need for a Savior because they understood what they were guilty of. The Word of God by the Spirit of God is (still) the method God uses to bring conviction of sin that leads to salvation. "Repent" - Peter’s preaching called for application. The Gospel is a call to action. For the Christian, repentance isn’t just an event at the time of our conversion, it’s part of an ongoing lifestyle. God calls people to Himself through the Spirit and through the Word.