The subject of sanctification often suffers either from neglect or from misuse. Some Christians have been taught that sanctification is optional. Others think that doctrines of justification and sanctification are pitted against one another as opposites. One is sweet and glorious – one is wearisome and laborious. What is the truth about our sanctification? How important is it? How does it work? The answer God gives in Philippians 2:12-13 reveals that our obedience is both a daily necessity and also a marvelous mystery beyond our comprehension.