When it comes to writing about Christianity, C.S. Lewis had an impressive talent for making claims that were witty, sincere, clever, pithy, and completely wrong. I discussed one of these – the “Lord, Liar, or Lunatic” argumentbefore. Recently, I’ve been seeing another one popping up in church ads on the Boston subway, where I do a lot of my writing. Lewis said:

One must keep on pointing out that Christianity is a statement which, if false, is of no importance, and, if true, of infinite importance. The one thing it cannot be is moderately important.

The church slightly modified this quote to fit in its ads: “Christianity, if false, is of no importance, and if true, of infinite importance. The one thing it cannot be is moderately important.” The modified version removes a little bit of the untruth: surely there is more to the two-thousand-year history of Christian tradition, from St. Teresa’s visions to church architecture, than a mere statement. But the “statement” bit isn’t the point of Lewis’s quote, and it’s not what I want to focus on here either.

Rather, there is something very wrong with the claim that Christianity, however one identifies its nature, is either of no importance or of infinite importance. It is no coincidence that those who make this claim – Lewis and the church advertising it – are entirely on one side of the presumed dilemma. They believe Christianity to be true, and therefore of infinite importance. That part is a perfectly defensible claim.

The problem comes on the other side of the dilemma. I am surprised at how little Lewis seems to have thought it through, given that he was at one point an atheist himself. There are many in this world who believe Christianity to be false. But the inference that it would therefore be unimportant is utterly bizarre. Many self-proclaimed atheists spend a great deal of time attacking Christianity. Are they wasting their time?

The question is entirely rhetorical. One might as well ask whether right-wingers who attack left-wing ideologies, or left-wingers who attack right-wing ideologies, are wasting their time. Of course they aren’t! For millions of people believe in each of those opposing ideologies, and the beliefs matter because the people matter. They’re real and they’re powerful. Left-wingers can tax you. Right-wingers can take away your health care and your children’s education. Left- and right-wing ideologies matter for this reason. That either ideology is true or false makes no difference to this importance.

Christians, meanwhile, can put you in jail for your choice of sexual partners. They can make it impossible for you to access abortion or even contraception. And they can fight for – and achieve – the equality of people of all races amid a society that denies it. In the past century, Christians of various sorts have done all these things many times, and done them because they were Christians: because they believed in, identified with and/or practised Christian tradition.

Beyond these political implications lies the historical memory of Christianity that continues to percolate through modern Western culture, a long set of influences we are often unaware of – the kind of influence that serious atheists like Nietzsche take great pains to uproot. And that’s not even to mention the beauty of Christian art and literature, so often appreciated by people who have no patience for Christian belief. All this is of no importance? Only to someone who has not thought seriously about what it is to believe Christian tradition false.

I am not taking a position here on the truth or falsity of Christianity, only on what is implied by its being false. Can a false Christianity be moderately imporant? If the answer is no, it is only because a false Christianity must be very important.