How To Change Direction 

If we are to change our direction, a new power is needed. For example, if I take a ball and throw it across the room, the ball will continue in a straight line unless some superior power averts it.  So too, natural human beings continue in certain directions, as Paul would have continued his persecution. Sinners would continue in their sin. Agnostics would continue in their doubt unless some superior power intervened. And that is the power of grace.