The power to witness comes from God.  It is by the power of God the Holy Spirit that any follower of Christ is effective in witnessing.

(Amplified) Acts 1:8 “But you shall receive power (ability, efficiency, and might) when the Holy Spirit has come upon you …”

  This promise was given to Jesus’ disciples before He ascended into heaven.  He promised to send God the Holy Spirit to them from heaven.
  Why is this promise important for us today?
  It is the power of God Who makes us effective witnesses.
  If you have been called by God to an organization which tells others about Jesus Christ – it will be by the power of God.
  If you have been called of God to witness (and all followers of Christ have) about Jesus Christ in the every dayness of your life…it must be by the power of God.

It is by God’s power
which gives the ability to effectively witness…

To witness: 
to know Jesus Christ and the power of His resurrection

~ and so change lives ~