For those trying to develop their spiritual side, will power can be both a blessing and a curse.  Willpower can help you stick with a schedule of practicing your spiritual development techniques, reading the books, listening to spiritual music, etc.  On the other hand, a strong will usually results in a strong ego that wants to maintain control of you at all times, and that prevents spiritual communication.  It can get tricky.
    So use a little will power to help you stick with schedules and do what you need to get done, but don't get carried away trying to build up a super will as some business gurus, for example, teach by having you do exercises like trying to hold your breath for a long time, like learning to tolerate pain, like walking on hot coals without getting burned, etc.  This type of development of super willpower only develops a super ego that will never allow your spiritual side to develop to any significant degree.