Well this is certainly a familiar verse. We've all read and heard it hundreds, possibly thousands, of times. And while familiarity doesn't breed contempt when it comes to scripture, it can dull our ears. Do you see the amazing promise in the above verse?
The Holy Spirit had not yet come upon those with Christ at his ascension, but the implication is that the Spirit will soon. We see this happen in stunning fashion at Pentecost. And when this occurs, they certainly "receive power." What sort of power is Jesus talking about? It is the power to unashamedly, boldly, and effectively proclaim the gospel. This happens immediately in Peter's case. He goes from denying Christ three times out of fear to preaching Christ crucified even when the religious leaders tell him not to.
This promise has a purpose. One of the primary reasons the Holy Spirit came was to empower Christians to be witnesses for Christ all over the earth. The Spirit is not limited to certain places, as if some locales or situations are too difficult for him. Instead, the Spirit's presence with all believers ensures that we have all we need to be effective witnesses for Christ wherever we go.
In just one little verse Jesus provides his people with both a promise and orders. The promise is of a person - the Spirit - who will make their evangelism efforts successful. The orders are to be faithful witnesses wherever and whenever.
This should give us great hope. The Holy Spirit is as alive and active today as he was then. Also, we have much easier means to get our witness to the ends of the earth. It is the church's responsibility to see that happen. Let's work together to make it so.