Matthew 23:3 NIV
So you must be careful to do everything they tell you. But do not do what they do, for they do not practice what they preach.
Do what they say, not what they do. It seems to me there are two lessons we need to take to heart from this chapter. First, we need to make sure we are not Pharisees. That is huge in itself, but the second lesson may be more difficult to accept. That is, truth is truth no matter who speaks it.
Our tendency is to write off anything that comes from a "heretic." If we find fault with an author, we won't read him anymore. If we're really serious then we won't even read someone who reads him. We call it purity by two degrees of separation. It is curious that Jesus didn't say, "The Pharisees are twisting and manipulating the law. Don't listen to them." Rather he said that the truth they speak is truth. People just need to be discerning enough to separate the truth taught from the error practiced.
Now, one could argue that they were not teaching falsehood, just practicing it. But that is not exactly the case. Jesus quotes some of the things they are practicing and teaching and says they are wrong. For example:
Matthew 23:16-17, 37 NIV
"Woe to you, blind guides! You say, 'If anyone swears by the temple, it means nothing; but anyone who swears by the gold of the temple is bound by that oath.' You blind fools! Which is greater: the gold, or the temple that makes the gold sacred? Jerusalem, Jerusalem, you who kill the prophets and stone those sent to you, how often I have longed to gather your children together, as a hen gathers her chicks under her wings, and you were not willing."
They are not only practicing a wrong understanding of the law, they are teaching it. Jesus followers are to be discerning, not ignoring and rejecting. Father, keep me from developing a critical spirit, but give me a discerning heart and mind. May I teach and live your truth.