Christians have complained for years about the secularization of sacred holidays. Non-Christians often sympathize: After all, they've seen A Charlie Brown Christmas too. Turning a celebration of Christ's birth into a festival of crass commercialization? Everyone can see what's wrong with that.

Sometimes, though, the dangers are a bit more subtle. What do we say when a holiday is hijacked not for money, but for a much-touted Good Cause? And when it's done not by the world, but by leaders in the church?

That's not a hypothetical question. It's happening right now. And not only with a single holiday, but with a holy season: Lent.

While Christians around the world spend Lent in prayer and penitence for their sins, a group of church leaders around the world are spending Lent promoting a "carbon fast" to fight global warming.

The campaign is spearheaded by some big names in Britain, including the Bishop of Liverpool, James Jones. "There is a moral imperative for those of us who emit more than our fair share of carbon to rein in our consumption," Jones declares.

So what do you do during a "carbon fast"? Well, they came up with 46 days' worth of ideas — some old, some new.

You still cut out meat — not for spiritual reasons, but for the environmental benefits. (Some people have done the math on how much cutting out meat could decrease our "carbon footprint.")

You do a lot of the old, standard conservation stuff: You recycle and carpool and turn down the heat and close the curtains and so on. You also do some of the new, trendy Go-Green stuff: You buy products with eco-friendly packaging and compost your food waste and get a low-flow shower head and unplug your cell-phone charger.

And you do stuff like this: "Pray that all countries will commit to tackling climate change and for rich developed countries to take responsibility and cut emissions fast." And "Remove one light bulb from your home and live without it for the next 40 days. This will decrease your energy use and act as a reminder of what you are doing during Lent."

Which raises the questions: Just what are they doing during Lent — and more importantly, whether it's good or bad in and of itself, what does it have to do with Lent?

Ask the carbon-fast campaigners and they'll say they're saving the world — especially the Third World, which is said to suffer most from "those of us who emit more than our fair share of carbon."

"This initiative shows there are ways we can make a difference that might seem like a sacrifice to begin with but can easily become part of everyday life and help tackle dangerous climate change," says Ed Miliband, the United Kingdom's minister for energy and climate change. (The "carbon sin" he says he'll miss most: Driving short distances into town.)

Ask some critics and you'll get a different answer.

"There was a time when a sin really meant something," says Frank Furedi, sociologist at the University of Kent. "These days, some theologians, including the advocates of a carbon fast, wouldn't recognize a moral sin if they bumped into one." Furedi, noting that actions that "can easily become part of everyday life" can hardly be called sacrifices, argues that "the carbon fast represents a semi-conscious attempt to transform environmentalism into a caricature of a religion."

The "only beneficiaries" of the fast will be "westerners who will feel better about their own lives, even as the lives of the supposed beneficiaries remain untouched," adds Chuck Colson of Prison Fellowship. "God may be calling us to live more simply — but it ought to be as an expression of our trust in Him, not fear of an environmental doomsday. This, in turn, will enable our concern for the least of our brethren to go beyond choosing paper over plastic."

How should we look at all this?

The answer doesn't hinge on whether we should believe in man-made global warming. Either way, at least some of the carbon-fast actions have merit in and of themselves: Conservation is a good idea in general, a part of biblical stewardship. But either way, the carbon fast has nothing to do with Lent. It's merely a marketing gimmick — hitchhiking on the pre-existing season of sacrifice to make us pay attention to the habits its sponsors want us to adopt.

Lent, after all, is a season of repentance for our rebellion against God. As a part of that season, some Christians give up some things they normally enjoy because it helps them focus on penance and sacrifice, which were ultimately accomplished on our behalf by Jesus Christ. The carbon fast doesn't focus our attention on that purpose at all. In fact, it distracts us from that purpose.

And there's something quite literally diabolical about that. The church leaders behind this idea may believe that they're promoting Christian stewardship over the earth, and even saving the world. But the devil has a bigger goal: to take men's eyes off Christ and turn them in any other direction — including toward a secular Good Cause. In fact, the nobler the cause sounds, the better that may be for the devil's purposes.

C.S. Lewis illustrated this in The Screwtape Letters, where a senior devil (Screwtape) tutors his nephew (Wormwood) in the arts of corrupting a man. The book was set in Britain around World War II, so naturally, Screwtape turned his attention to whether to make a particular man (a recent Christian convert) into an ardent patriot or a fervent pacifist. Either option would do, Screwtape said — so long as the man placed the cause ahead of Christ.

Let him begin by treating the Patriotism or the Pacifism as a part of his religion. Then let him, under the influence of partisan spirit, come to regard it as the most important part. Then quietly and gradually nurse him on to the stage at which the religion becomes merely part of the "Cause," in which Christianity is valued chiefly because of the excellent arguments it can produce in favor of the British war effort or of pacifism.

You can see where he's going with this, but Screwtape spells it out:

Once you have made the World an end, and faith a means, you have won your man, and it makes very little difference what kind of worldly end he is pursuing. Provided that meetings, pamphlets, policies, movements, causes and crusades matter more to him than prayers and sacraments and charity, he is ours — and the more "religious" (on those terms), the more securely ours. I could show you a pretty cageful down here.

During Lent, of all times, we shouldn't stumble into that trap. And we won't, so long as we keep our eyes fixed firmly on Jesus — and refuse to look anywhere else.