https://www.mljtrust.org/sermons-online/acts-4-18-20/saved-to-serve/

When the apostles met the risen Christ, they were transformed and empowered with boldness to proclaim the gospel to all that they could. Before the outpouring of the Spirit at Pentecost, they were fearful and timid but after they were fearless in their mission. In this sermon titled “Saved to Serve,” Dr. Martyn Lloyd-Jones explains this change enabled them to stand against the Jewish leaders when they refused to cease preaching the gospel of the risen Christ. This is no ordinary boldness, but it is a result of the new nature that is brought about by salvation and regeneration. As the gospel transforms Christians, they are given the Holy Spirit and filled with its wisdom and guidance. The apostles in Acts could not stop preaching the glory of Christ. They were no longer the weak and fearful men who were hiding in the upper room. They had received the new life that the gospel brings and they fearlessly proclaimed the gospel message. Christians have a new source of life and wisdom when they are made anew in Christ. They are motivated to bring the gospel to this broken and sinful world. It is this hope in the new life in Christ that compels Christians to share the gospel with all to the praise and glory of Jesus Christ.