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Nothing contributes so much to tranquilizing the mind as a steady purpose-a point on which the soul may fix its intellectual eye.
— Mary Wollstonecraft Shelley

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Calm comes from having a clear aim, the passage says. A steady purpose gives the mind something to settle on, like a point the soul can look at with its 'intellectual eye'. The metaphor pictures focus as a steady gaze that quiets restlessness.
Context reviewed