"Harry has been through a terrible ordeal tonight... What he needs now is sleep, and peace, and quiet." - Albus Dumbledore
The Four of Swords shows a time of rest and recovery. It allows one to meditate and contemplate a situation without hurry.
Throughout his years at Hogwarts, Harry has found himself in the hospital wing rather more times than he would like. It is kept as a place of peace and healing, where one could rest while their injuries mended without having to worry about the stressful factors in life.
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