In the 1570s, a Spanish Carmelite nun named Teresa of Ávila sat down to answer a hard question: what actually happens to a soul on its way to God? She wrote her answer as a single, startling image. Picture the soul as a castle, she said, built entirely of crystal or diamond, with the King already living in a room at its very center. Most of us wander that castle for years without ever going in. We stay in the courtyard, distracted, half-aware there's more to find.

Teresa called her book The Interior Castle, and it maps seven "mansions," seven rooms a soul passes through on the way inward: from a first shaky awareness of God, through failure and perseverance, through the quiet danger of thinking you've already arrived, into a kind of prayer that can no longer be earned, only received, and finally into a union so complete that the soul and its King are, in her words, no longer easy to tell apart. She wrote from experience, not theory. The book is four hundred and fifty years old, and it's still considered one of the most precise accounts of the inner life ever put on paper. The Church later named her a Doctor of the Church, one of only a handful of people in two thousand years given that title, for exactly this reason.

Seven Mansions takes this journey and re-tells it in the form of an epic fantasy. Ines Vael, a wall-mender's daughter with a secret she's kept for years, enters an order that can see what feeds on what a soul refuses to confess. Across seven novels, she moves inward exactly the way Teresa describes, one castle, one war, one mansion at a time, and every battle she fights is really the same battle Teresa wrote about: not a monster at the gate, but a soul deciding how far in it's willing to go.

You don't need to know a page of Teresa's actual book to read this series as a fantasy adventure. But if you do know it, you'll find her whole map hidden in plain sight, in the walls, the reptiles, the wounds of love, and the King waiting at the center of every castle in the story.