Woe to you, scribes and Pharisees, hypocrites! For you clean the outside of the cup and the plate1, but inside they are full of greed and self-indulgence. You blind Pharisee! First clean the inside of the cup and the plate, that the outside may also be clean.While I thought it was a good sermon, it didn't hit me through the heart like a great sermon does. After some reflection, I realized that this is because I tend to make the opposite error of the Pharisees: I clean the inside and neglect the outside. I'm so focused on seeking internal transformation (often by inspiration) that I don't do the hard work of actually reshaping habits and living differently. The result is that while on the inside I may be coming to resemble Christ, on the outside (which is all anyone else sees) I look little like Him in many ways.
There's a misconception in Christianity that makes this opposite mistake easy to miss, saying that the inside, the heart is all that matters. Jesus transforms you on the inside, and the outside changes to match. But I don't think it's quite that simple. He didn't say, "Clean the inside and the outside will also be clean", but "Clean the inside...that the outside may also be clean." Internal transformation is vital and preeminent for the Christian, but it is no excuse to be lazy about changing the patterns of how we actually live--it is an opportunity to do so.
1 Random aside: I had an instructive example for a "wrong message" to take from this woe. If you try to be practical and preach a sermon based on this text asking whether you are a cup or a plate, and enumerating bullet-pointed differences between cups and plates, you are probably, as Jesus had just said, "straining out a gnat and swallowing a camel". The point is the difference between cleaning the inside and the outside, not between Jesus' metaphorical cup and plate.