Could you remind me how the Trinity works? And could you explain to me again this idea of grace?" One diligent student had no problem grasping Islam. She had no problem understanding religions based on a concept of exchange—do something for a god and he'll do something for you. But she was legitimately confused about Christianity: "The Quran is simple. Why is Christianity complicated?"

April is not the cruelest month when it includes Easter. It's great to read the Bible on mornings that are becoming warmer. I remember good evenings putting my children to bed with Sylvia Plath's The Bed Book, which praises many fanciful kinds of sleeping areas but condemns one: the "white little, tucked in tight little, nighty night little, turn out the light little, bed."

We could assess religions the same way: Tucked-in-tight religions are too symmetrical to be true. Take the smooth explanations at the website everymuslim.com. We're told that "Almighty Allah, when depriving a person of a certain ability or gift, compensates him for it, by bestowing upon him/her another gift." For example, "People who are deprived of sight have very sensitive ears."

So it all makes sense: No sight, no sweat, Allah compensates. Hinduism's doctrine of karma is also clear: If you're blind in this life, it may be because you broke someone's glasses or didn't give money to a sightless beggar in the last one.

Many Jews 2,000 years ago desired such clarity. Some asked Jesus to choose between two logical possibilities: Was a man blind because he sinned or because his parents sinned? But in chapter 9 of the Gospel according to John, Jesus explains, "It was not that this man sinned, or his parents, but that the works of God might be displayed in him."

How are those works displayed? Maybe a miracle gives sight to the blind man. Maybe a miracle occurs in other people, as they abandon natural selfishness and sacrifice to help a person in need. Sometimes we're stuck with mystery. Dorothy Sayers called Christianity the only religion that gives value to suffering—whether physical or spiritual—by affirming its reality and the opportunity to wrench some good out of it.

It would be great to understand mystery, but 19th-century pastor Charles Spurgeon put it rightly: "Providence is wonderfully intricate. Ah! You want always to see through Providence, do you not? You never will, I assure you. You have not eyes good enough. You want to see what good that affliction was to you; you must believe it. You want to see how it can bring good to the soul; you may be enabled in a little time, but you cannot see it now; you must believe it."