In his book Joy Unspeakable, Dr. Martyn Lloyd-Jones states, "Go through Acts and in every instance when we are told either that the Spirit came upon these men or that they were filled with the Spirit, you will find that it was in order to bear a witness and a testimony." That's your witness for Christ in power.
The gospel of Jesus Christ is the power of God unto salvation (Romans 1:16). The gospel comes not in word only, but through the power of the Holy Spirit. "For our gospel did not come to you in word only, but also in power, and in the Holy Spirit and in much assurance" (1 Thessalonians 1:5). As we witness for Christ, leave the results to the Holy Spirit.
The gospel is the power of God through the Holy Spirit. He uses our witness for the gospel of Jesus Christ. People are saved, when the gospel is heard in the Word and Spirit. Jesus said, "But you shall receive power when the Holy Spirit is come upon you, and you shall be witnesses to me in Jerusalem, and in all Judea and Samaria, and to the end of the earth" (Acts 1:8). Our witness for Christ is effective, through the power of the Holy Spirit.
God will use us to witness for our Lord Jesus Christ. We depend upon the power of the Holy Spirit. We give all the glory to God for those who are saved. We recognize our total dependence upon the Holy Spirit. God will use us to witness for Christ, through the power of the Holy Spirit.