Last week, we talked about the curious taboos that marked the Old Testament.

Such taboos are not really very strange to us if we think about it, which is why you did not start your day with a heaping helping of nutritious insect larvae, despite the fact that they are perfectly healthy to eat.

My point was that God has taken this natural impulse to say “Ick” — to regard certain things as “defiling” — and, as with many other natural things, raised it by grace to teach a spiritual lesson. The image of food too gross to eat and things too disgusting to touch was and is an apt image of sin, which sickens the soul much as maggots sicken the stomach. The problem is, it’s easy to confuse the image for the reality. That is why Jesus had to starkly instruct his followers that it was not food that defiled, but sin.

The beauty of this ugly image is that it really does communicate the social nature of sin, something that is lost on many moderns. The common belief sounded in our culture is, “Who cares if somebody sins in private? It doesn’t hurt anybody else!” But the reality is that spiritual pollution, like physical pollution, is everybody’s problem.

The funny thing is that those who deny the reality that sin can pollute a culture have no problem seeing that hydrocarbons can pollute an atmosphere. Those who are often most acutely sensitive to the dangers of exposing a region to electromagnetic radiation have no problem exposing that same region to electromagnetic radiation known as “the lyrics of the latest cop-killer rap” or a degrading TV show. Such people are oblivious to the fact that sin is a sort of “air pollution” too and that what we exhale in private is inevitably inhaled elsewhere.

Take Madonna. I’ve never bought a Madonna album, never attended one of her concerts, never seen any of her (reputedly terrible) films. But I know all about her. So do you. We know all about the various blasphemies, the various incarnations and transformations from Material Girl to Crucified Dance Diva. You can’t get away from her. She’s in the very air we breathe.

Our kids can’t get away from this stuff either. In a classic column, Peggy Noonan described the culture in which the Columbine killers — and we — live. The air is full of:

“... was found strangled and is believed to have been sexually molested ... had her breast implants removed ... took the stand to say the killer was smiling the day the show aired ... said the procedure is, in fact, legal infanticide ... is thought to be connected to earlier sexual activity among teens ... court battle over who owns the frozen sperm ... contains songs that call for dominating and even imprisoning women ... died of lethal injection ... had threatened to kill her children ... said that he turned and said, ‘You better put some ice on that’ ... had asked Kevorkian for help in killing himself ... protested the game, which they said has gone beyond violence to sadism ... showed no remorse ... which is about a wager over whether he could sleep with another student ... which is about her attempts to balance three lovers and a watchful fiancé ...”

“This,” says Noonan, “is the ocean in which our children swim. This is the sound of our culture. It comes from all parts of our culture and reaches all parts of our culture, and all the people in it, which is everybody ...”

Which is why God chose to use the image of pollution — of some all-soiling, all-pervading contaminant, like an infectious agent, or cooties, or leprosy, or sewage-stained water — to portray what sin is and what it does.

Because sin is not something that happens in private.

It is not something we can keep to ourselves. It inevitably gets out, like the ebola virus, and wreaks havoc with the whole of human society.

This pervading polluting quality of sin is also why Christ refused to make the cure for it — mercy and forgiveness — a purely private and individualistic affair.

Instead of simply saying, “All you have to do is pause briefly where you are, tell God you are sorry for your murder, theft, adultery and blasphemy, and then go on free as a bird,” he insisted upon instituting the sacrament of reconciliation — so that the social body harmed by sin can participate in the healing of that sin.

And so that very body can be the means by which the sinner is brought back into a love relationship — not just with God, but with the people he has harmed.

Mark Shea is senior content editor

for CatholicExchange.com.