We often hear that Jesus gave up power, and in many ways this is absolutely true—the Incarnation was a stunning self-limiting on the part of the eternal Son of God, and it went all the way, as Paul says in Philippians 2, to the point of death on the cross. Death is the end of all power, and the Son who is in very nature God emptied himself of all power on the Cross. That is a central part of the Christian story.
But while the whole gospel revolves around that moment of utter surrender and trust at the Cross, the New Testament writers also go to great lengths to emphasize Jesus' power in his teaching and healing, and the way he conferred that power upon his disciples both before and after his death and resurrection. And the resurrection, of course, is a breaking in of creative power like the world had not seen since the first moment of creation, and maybe even not then. The resurrection of Jesus from the dead has had more profound cultural effects, for longer, among more people, than anything else in history. That is power!
So I think the harm in only speaking of powerlessness as the Christian calling is that it does not take a lot of the New Testament seriously. For example, the part where Jesus gives his disciples authority to preach the gospel, heal the sick, and drive out demons. There is no doubt that we are called to exercise our power in a different way from the world (Matthew 20:25-26). But I see very little in the New Testament that implies that Christians should be powerless in a categorical sense. Instead, we are called back to the deep, true power that comes from bearing the true image of God in a world full of idols and injustice.
First, there are all sorts of power that don't come from exercising authority, influence, or leadership: The power of being physically attractive. The power of inherited wealth. The power of being born with a certain passport or speaking a certain language. The power, in a culture that reveres elders, of being old. The power, in a culture (like ours) that reveres youth, of being young. None of these really come from any kind of leadership, but they are all forms of power for better and for worse.
The other reason is that we all want to believe we are using our power well. But the Christian view of the world suggests that it is exactly when we think we are doing well that we are most at risk of playing God in the worst way. I not only wanted to write about the real gift of power, but the real dangers of power, which I summarize in the book as idolatry and injustice. And the truth is that authority, influence, and leadership, which all sound pretty benign and beneficial, can end up underwriting terrible idolatry and injustice. The best word for the whole beautiful, complicated, dangerous subject ispower.