Most people appeal to mystery at some point in their theology. And that’s what we would expect given that we’re trying to understand the infinite, transcendent, and ultimately incomprehensible God of the universe. So we end up talking about things like the Trinity (three persons in one being) and the incarnation (divine and human in one person), fully aware that we are affirming truths that transcend our understanding, but unwilling to say that they are mere contradictions. So we call them mysteries.
But what exactly does it mean to say that something is a “mystery” in theology?
In their book, The Mystery of God: Theology for Knowing the Unknowable (Baker, 2012), Steven Boyer and Christopher Hall explain that “mystery” is actually a rather slippery term in theology. So they offer a helpful taxonomy of different kinds of mystery, arguing that only the last is really adequate to a God who both transcends knowledge and makes himself truly known.