Saying "God has reasons we can't see" makes God unknowable and excuses anything

What skeptical theism says

Skeptical theism is a response to the evidential problem of pointless suffering. It says that because God's knowledge vastly exceeds ours, our failure to see a reason for some evil isn't good evidence that there is no reason. Stephen Wykstra and Michael Bergmann are among the philosophers who have developed this view. It's skeptical not about God, but about our ability to judge God's reasons.

Doesn't it make God unknowable?

Not necessarily. There's a big difference between not knowing God's specific reasons for a particular evil and knowing nothing about God at all. A child may not understand why her parents take her for a painful injection, but she can still know they love her, based on everything else she knows about them. Christians claim to know God's character not from working out the reasons behind every event but from other evidence, especially the life, death and resurrection of Jesus. If God came close enough to suffer with us, that is good reason to trust him when we can't see what he's doing.

Does it excuse anything?

The worry is that skeptical theism becomes an unfalsifiable "get out of jail free" card. That's a fair concern. But it's not as if anything goes. Skeptical theism doesn't claim that evil counts for nothing. It claims that one particular inference, from "I can't see a reason" to "there is no reason," is weaker than it looks. Evidence about God's goodness still matters, and so do other arguments for and against God.

Does it undermine morality?

Some critics argue that if we can't tell whether an evil leads to good, we'd have no reason to prevent it. But our moral duties don't depend on knowing the long-term outcome. We know we are called to love our neighbour, protect the vulnerable and resist injustice. God may have reasons to permit something that we, with our limited role and knowledge, are clearly obligated to stop. A parent may allow a child to struggle in ways that a stranger should not.

A fair concession

Skeptical theism can sound like a way of ending the conversation. Used carelessly, it can feel dismissive of real pain (see Explanations feel cold when you're hurting). It works best as one part of a bigger response, not as the whole answer.

How to explain this to a friend

A helpful picture for a friend is a doctor or a parent. We often trust people we know well even when we can't see their reasons in a particular moment, because we have evidence of their character elsewhere. Then you can explain that Christians ground their trust in God's character in Jesus, not in being able to explain every event. That shows the view isn't a dodge but a reasoned kind of trust.

The bottom line

Not knowing God's specific reasons for a particular evil is different from knowing nothing about him. Christians trust God's character for other reasons, especially Jesus, and that trust can survive not seeing the whole picture. For more, see The problem of evil.