Twilight in the cell as twilight in the heart
Wilde uses this comparison to describe the prisoner's life in a cell. The twilight in the cell mirrors the twilight in one's heart, meaning that the prisoner's sorrow is never-ending, just like the twilight in a cell.
Wound that bleeds metaphor
Wilde compares his feeling of sorrow and despair to a wound that bleeds when any hand touches it, even that of love, but when the hand of love touches it then it doesn't bleed in pain. He calls the sorrow the most sensitive of created things.
Humility like a treasure in a field simile
Wilde came to the realization that nothing in life is meaningless. The suffering is the least meaningless things of all. He discovered in his nature a feeling of humility and compares it to a treasure in a field. It is this humility that makes him think of Christ and come to the conclusion later on that his suffering is only a path to a wonderful new beginning.
Living life safe from sorrow as living life at the sun-lit side of the garden simile
Wilde realizes his mistake of trying to escape from sorrow of life. He describes his life as being confined to the sun-lit side of the garden and ignoring the other shadowy side. He tried to escape from that which he realizes now makes him see the true beauty of life and art.
