Purple linen symbol
Purple linen is mentioned by Wilde as a symbol of luxury, of high rank and indulgence in materialistic things. He describes no longer needing the purple linen to feel as a complete and confident individual.
Christ as a symbol
Wilde uses the image of Christ as a symbol of individualistic completeness. He compares Christ and his life to poetry. Thinking of Christ helped Wilde realize that his sorrow is there for a reason, and that there is life and love after such sorrow.
Morality, religion and reason
Wilde in his letter describes that neither morality nor religion nor reason can help him. Morality does not help him because he is one of those who are born in exception to it. Religion does not help him because he does not believe in the unseen, only what he can feel. Reason does not help him because it makes him think that what happened to him is unjust. It could be said that these three factors hold the most importance in society, and in the fact that these factors can't help Wilde they symbolize his role as a societal outcast.
Child symbol
A child symbolizes the human truth, the reality of what a person is and what one should strive to be. Children are simple and honest without the pretenses of any sort of rules; therefore, to become completely oneself, to connect with one's soul, one becomes as simple as a child.