The title focuses on the precarious balance Christians experience between heavy involvement and no involvement in politics. Colson's thesis seems to be that Christians need to maintain a balance - being in the world while not being of the world and Christians must be a light to the world and salt of the earth.
Colson uses the examples of Christian involvement (and lack of) in resisting Hitler, Marcos, and other brutal figures in history to illustrate the importance of Christians being involved in the political process without being consumed by the power that goes with politics.
Read and be encouraged to be rightly involved in politics while remembering that ultimately we are citizens of another kingdom to come that will last forever!