Sin proceeds in one direction, but defilement is a two-way street.

C.S. Lewis said that “good and evil both increase at compound interest.”* He did not attach that insight to a particular Bible text, but I would like to supply one. In Matthew 15.1-20,  we find the well-known passage where Jesus is rebuked by the Pharisees for allowing his disciples to eat with ceremonially unwashed hands contrary to the tradition of the elders. Jesus agrees that rebuke is in order –but it is to the Pharisees for exalting their traditions above God’s commandments, effectively negating them. (Mat 15.3-5.) There is a lot going on here, but the part I want to focus on is Jesus’ corrective to the theology behind the elders’ tradition of ceremonial washing before meals. Jesus says, “Not what goes into the mouth defiles a man; but what comes out of the mouth, this defiles a man.” (Mat 15.11.)

This is one of those verses we get so well that we don’t get it. We get that Jesus is distinguishing between the inner and the outer and clarifying that sin originates in the former, not the latter. But that does not mean that the connection between inner heart and outer action is a one-way street, which is what we tend to assume. We get the causal connection between the heart and behavior, but we tend to miss the connection between behavior and the heart. Jesus says, “What comes out of the mouth, this defiles a man.” (Emphasis added.) Now whatever sin comes out of the mouth was first in the heart. So the heart was already defiled. But Jesus says a further defilement occurs when the sin is allowed to come out. So while sin proceeds in one direction, defilement is a two-way street. When we have sin in the heart, that is bad, but when we let it come out, that is worse — not only for whomever it is aimed at but also for us who aimed it. We victimize ourselves as well as our target. Our heart is changed for the worse. So keeping our heart with all diligence, as Proverbs 4.23 instructs us, means guarding what goes out of our heart as well as what goes into it.

As an aside, let me note that Jesus does not say that whatever goes into us cannot defile us; he says whatever goes into the mouth cannot defile us because it goes into the stomach and is passed on. (Mat 15.17.) By implication, what goes into the heart can defile us. And as we have just seen, whatever comes out of the heart can defile us as well.

How exactly is our heart defiled when we let sin come out? God only knows the sum of it. But at a minimum, it will be a lot easier to let sin out the next time — or perhaps we should say that it will be a lot harder to keep it from coming out. The good news is that this process also works in the other direction. When we do what is good (regardless of what is in our heart), it will be a lot easier to repeat that good in the future. Our heart will have been changed for the better. So when we have sin in the heart, the first order of business is to not let it out, and the second order of business is to instead do what is good.

But isn’t that hypocrisy — having one thing in the heart and doing something else? Not necessarily. It depends on why we have one thing in the heart and do something else. If it is to manipulate someone, to gain some advantage, to make them indebted to us, that is hypocrisy. If it is to keep from compounding the sin in our heart by refusing to let it out, that is holiness.

[And t]hat is why the little decisions you and I make every day are of such infinite importance. The smallest good act today is the capture of a strategic point from which, a few months later, you may be able to go on to victories you never dreamed of. An apparently trivial indulgence in lust or anger today is the loss of a ridge or railway line or bridgehead from which the enemy may launch an attack otherwise impossible.**