If the journey of prayer, which ought to become increasingly continuous, is the journey into the interior points, and toward the innermost and uppermost point, of the spirit, then we travel from the exterior, where God is present, to the interior, where God dwells.
We pass from the exterior wall of Saint Teresa’s castle to the interior. We pass from room to room, seeking the voice we’ve heard at the centre. We open doors. Once the doors remain open, we can pass more easily from one room to another, as our action requires, as our thinking requires, and as our prayer requires. The opening of some doors, which have rusted, is painful to the soul: we sometimes call this, along with John of the Cross, a “dark night”. Creaky, rusty doors are painfully opened. But once the doors are open, grace can flow through and fill the rooms.
The goal is to find the centre room where the Bridegroom dwells. He sets up his tent more in one place than another. He sets up his tent at the centre, which is also at the height of the soul. Once that door is opened, water from the living fountain (for the Bridegroom is also an endless fountain) flows downwards and outwards into all the other rooms. Why? Of course, the doors have been left open. Just to open the doors was one grace. But the marriage at the innermost and uppermost room has the goal of pushing a flood into all the other chambers. Of course, progress can still be made. Other doors can still be found and opened, gaining access to new chambers which will immediately be filled with the flood. There still exist even some of those painful rusty doors. But the main thing has been achieved: the innermost, uppermost room has been found, its Bridegroom has been found, we have left behind our attachments to the other rooms, and the Living Fountain has been allowed to erupt like a volcano into all the open pathways and through all the open doors.
This is what the saints mean by “dark nights” and the “interior castle”, the necessary of detachment (from the other rooms to be free to find the centre room), the “mystical marriage”, and the fact that suffering can continue even after that marriage, though it is the far greater goal in this life.