The Book of Acts shows how Jesus continued His work through His followers after His ascension. Every Christian is commissioned to be a witness, sharing the simple Gospel message about Jesus Christ. This witnessing happens at multiple levels - in our immediate community, our broader region, and the entire world. The secret to effective witnessing is the power of the Holy Spirit, who indwells believers at salvation but requires daily surrender. There is no retirement from Christian service, as believers of all ages have valuable contributions to make in fulfilling the Great Commission.