The resurrection of Jesus was God’s seal and act of approval signifying that His death was sufficient. Jesus never resurrected Himself – God raised Him from the dead. God the Father was pleased, and satisfied with His victorious life and death. In raising Him from the dead, God gave testimony that all was satisfactory.
In Acts 1:8, the Lord is not using the word “witness” to refer to someone who gets up and gives a testimony. He is referring to a person (with the power of the Spirit upon him) who is willing to let his life be slain in order that the life of Christ may be lived through him. Subsequently, he becomes a witness or a testimony of the power of God.
Jesus’ disciples were a witness because they operated in the power that God used to raise Jesus from the dead. When did Jesus tell His disciples, “I will pour the Holy Spirit upon you?” It was after His resurrection, for now there was a resurrection quality in the power that was to come upon them. As a result, the disciples always ministered in resurrection power.
Our lives are also a witness of the Holy Spirit’s resurrection power. You might ask, “How can that be?” It is so because the same power that raised Jesus Christ from the dead, now dwells in us! We have access to this power because God dwells in us through His Holy Spirit. As we do the work God has given us to do, He enables us with power that exceeds our comprehension and expectations.