John 15:27
And you also are to testify because you have been with me from the beginning — the disciples are called to join the Spirit in testimony; they are eyewitnesses to Jesus' ministry and will bear witness to what they have seen and heard. The phrase "from the beginning" places them in the position of those who knew Jesus from his first calling of disciples, who have accompanied him through his public ministry and now accompany him in the upper room. Their testimony, combined with the Spirit's testimony, creates a weight of evidence that the world cannot refute, only reject.