Jesus knew He was to leave the earth, so He told His disciples He would send someone of importance to be with us. (John 16:7) It was the Holy Spirit. Soon after their baptism in the Holy Ghost promised by Jesus (Acts 1:5) they received the promised ‘power’ (Acts 1:8) and became witnesses. Witness means: Testimony; That which furnishes evidence or proof; A person who knows or sees any thing- an eyewitness. The disciple’s lives would never be the same again.
First recorded in the book of Acts after their baptism is that they spoke testimony of what they had seen in Jesus and His life. At the same time, this spoken testimony- given by many disciples- was accompanied by a gift previously unheard of- speaking in other languages which must have been seen as somewhat miraculous. This astounded the listeners, and made them believe what was being spoken. It is no wonder that 3000 became believers that day given the testimony with the power of the Spirit evident in it. The rest of the book of Acts is just what it is called, the Acts of the Apostles and other believers- in other words, the things that they did. See, we are not meant to be fed more and more Bible truths only to keep it unto ourselves. Instead, we are to act upon what we learn by putting it into practice in this dark world thus shining His light into the darkness.
We are to give testimony by our words, our actions, our behaviours and morals, even our motives and intentions. When people see the good changes in us or find us to be of good character showing the love of God continually and our lives filled with the power of the Spirit, they are more likely to desire what we have, and they just may want to know this Jesus of ours. Increasing our knowledge does not necessarily increase our actions upon it. We need to act on the knowledge we already have.
The Word of God, the testimony of Jesus in our lives and the power of the Holy Spirit combined make for a persuasive witness to the truth of who Jesus is and can be in the lives of those around us. The world will want what we have when we start ACTing the truths in the Word and they see His power in our lives.