No one needs to teach us Pharisaism. Like all sins, it comes naturally enough if we do not guard against it. But you are Christians, you are a new creation in Christ, and one of the glorious characteristics of this new creation is the desire to guard against all such sins.
One of the most deceptive features of Pharisaism concerns this matter of deception itself. Many have come to believe that a lie is something that can only come out of your mouth. It is in the interest of Pharisees to have a very literal, and very wooden, and very limited, definition of lying. But a man can lie by saying nothing. A man who makes anonymous accusations is a liar, because he is causing suspicion to fall on others. A man can even lie by telling a selected version of the strict, literal truth. Suppose one of you students wrote home that worship this week was very good, and that Mr. Wilson delivered his sermon while sober. All of it true, and deliberately misleading.
Further, the Bible tells us that we are not to lie to one another, seeing that we have put off the old nature with its evil practices. The ninth commandment prohibits bearing false witness to your neighbor.
We see from this, and other examples in Scriptures, that deception is an act of war. There is such a thing as lawful deception—think of the Hebrew midwives, or of Rahab, or of David. The most holy God deceives His enemies, and I doubt that any of you—if you have had a friend or relative serving in the military—have taken him aside to rebuke him for his camo gear. “You are telling your enemy that you are a bush when in fact you are not a bush.”
We are not to trifle with this, because the lake of fire is reserved for liars. We not just to tell the truth, we are to live the truth. We are not just to live the truth, we are to fight for the truth, and to take our stand against all lies and liars. But as with all such things, our definitions of must come from the Scriptures, and not from the traditions (and lies) of men.