Catholics believe that the Holy Eucharist that they receive at Mass is the body and blood of Christ — not just a reenactment or a symbol, but the true substance of Jesus Christ, only with the visual appearance, taste, smell, etc., of bread. In other words, we believe that when Jesus said, "This is my Body," he meant it literally. And then, when he said, "Do this in memory of me," he also meant that literally. So to this day, we do it at every Mass.

Once you accept that premise, reception of the Eucharist is literally communion with God. For that 10-minute period before what appears to be bread has entirely dissolved into your stomach acid, you physically carry Jesus inside you. This act also entails a certain unity with all the other communicants. You're coming together of one mind and heart for the purpose of joining Christ himself, reliving and reaping the benefits of his sacrifice on the cross.

So, the Eucharist is kind of a big deal in Catholicism.

Take that into account when you think about the current controversy over whether church authorities will or should deny Communion to House Speaker Nancy Pelosi or any other Catholic politician who publicly defies the church's doctrinal or moral teachings on serious subjects such as abortion. The archbishop of San Francisco has taken this step with respect to Pelosi. The archbishop of Washington, D.C., has not, at least not now.

You may be asking yourself, does this happen often? The answer is no — it is, by necessity, extremely rare. For most people, it would be impossible to enforce it, let alone to do so justly. For most people, when you go to Mass, you're on the honor system. If you're not supposed to go to Communion, you know not to. To get special treatment, you have to be quite famous, and you have to have done something really, seriously bad that everyone knows about.

Just to step back a moment, it is worth looking at the separate issue of who can receive Holy Communion.

In the Catholic Church, only baptized Catholics who have been instructed in the sacrament's meaning (usually as children) are permitted to receive the Eucharist. In the Roman Church, children typically must also make their first confession before their first Communion. (Some Eastern Rite churches give Communion to infants at baptism.) In addition, Catholics must be free of unconfessed mortal (i.e., serious) sin, have fasted an hour beforehand, and not be under any sort of ecclesiastical sanction that forbids taking Communion.

With respect to mortal sin, that's something that Catholics police themselves on. Mortal sin requires not just an evil act, but a certain state of mind and completeness of knowledge, of which only the sinner himself can be fully aware. No one but God can ultimately judge your personal culpability. So for Communion, you're on the honor system, so to speak.

Under what circumstances will church authorities actively withhold the Eucharist from you? They explicitly cannot do it for sins that are not widely known. But Communion can be withheld if you are known by local church authorities to be under a formal sanction, such as excommunication. Another reason, even if you are not under such a sanction, is that you are obstinately persisting in a public or notorious state of sin, such that, whatever your personal culpability, you are causing scandal.

For example, you could be publicly denying the Resurrection and encouraging others to do so. You could be openly cohabiting with someone who isn't your spouse. You could become known in public as a member of the Ku Klux Klan. Even then, unless you are sufficiently famous and your disruptive, grave sin is sufficiently public, your local bishop is unlikely to pass around your photograph and instruct priests and ministers to withhold the Eucharist if they see you. You are barred from Communion, but like everyone else, you're on the honor system.

But then, there's the Pelosi scenario.

Let's say you are the second-most famous Catholic in America. You have a habit of flaunting your Catholicism as part of your political schtick — claiming, for example, to be "an ardent, practicing Catholic" in television interviews. You openly reject the church's teaching on such a critical moral issue as the sanctity of human life from conception to natural death, the flouting of which church authorities consider to be one of the grave injustices of our age.

So, what then?

Although Pelosi's level of personal culpability is her own business and God's, the scandal from her external actions is the reason something like this might be appropriate. To have such a person just show up at Mass and take Communion, as if there's nothing wrong, is to give the impression that this is OK by the Catholic Church. It screams out, "Hey, don't worry — we're not really serious about all that stuff we do and teach."

Worst of all, the uncritical acceptance of someone of Pelosi's stature would make it seem acceptable for others to follow her example — outwardly endorsing and voting for and promoting a grave evil while going through the motions of living their faith.

So there are very few people for whom such a sanction could be appropriate. But Pelosi is definitely one of those rare cases.

Should the bishops do this? It's not really my place to say. The rationale for it seems clear. There are also drawbacks. For example, it has a way of creating a big political controversy every time Pelosi goes to church — you're not supposed to go to Mass so that you can get upset about your fellow parishioners' shortcomings; you're supposed to be upset about your own. Pelosi can also make a mockery of the thing by presenting herself for Communion in public outside of her diocese, someplace where no formal sanction has been imposed; Pelosi has already done this, in fact.

Then again, that might be a feature, not a bug. Perhaps the deprivation of Holy Communion surrounds a controversial Catholic with an appropriate amount of controversy. Maybe that's what's needed, instead of just going along to get along.