" . . . He [Christ] began to say to His disciples first of all, 'Beware of the leaven of the Pharisees, which is hypocrisy.' "
Our Redeemer prioritized this teaching (re. the pharisees and their hypocrisy) because He knew that it could, and would destroy His followers if it was not addressed head-on. The pharisees' "leaven," (or teaching) is dangerous, because it seeks to seduce the soul into smug self-righteousness.
Christ's worst opponents (by far) were the pharisees--the very ones who were the most religious and devout. Jesus reserved His harshest words for them; and He warns us (even today) to watch out for their poison, (which, like the snakes the Lord compared them to, comes from their lips).
[Puritan quote of the day: "God does not bring His people into troubles, and leave them there." --Thomas Watson, in "All Things for Good"]
