You can draw several lessons from the story. You could sum up the more evident ones in these themes:
Looks can be deceiving. People are not always what they seem to be.
Infatuation is a very elusive and ephemeral thing without substance. Love, however, is always true and stands the test of time.
Before making sacrifices, count the price. Don't throw away your life for people or things that aren't worth it.
A sad story about undying and altruistic love, "The Nightingale and the Rose" is essentially a parable that reads like a romantic story, and is presented as a fairy tale. In typical Wilde style, the narrative is injected with irony, sarcasm, paradox, and surprise. These are all conduits that deliver the same message: There is no fairness in love or life.
The Nightingale represents the dreamers. Those who decide to love for love's sake and are willing to give up everything to live up to that standard. The bachelor student is also a dreamer, but a shallow and petulant one who does not really suffer the way that he says he does: for the love of a young woman who refuses him unless he gives her a red rose.
The Nightingale, as a martyr for her cause of love, goes from rose tree to rose tree tree in search of that red rose for the allegedly love-striken man. The red rose would come at a very high price: the life of the bird. For this reason, the Nightingale feels that to sacrifice for a principle that she truly abides by makes her belief even stronger.
If you want a red rose,' said the Tree, 'you must build it out of music by moonlight, and stain it with your own heart's-blood. You must sing to me with your breast against a thorn. All night long you must sing to me, and the thorn must pierce your heart, and your life-blood must flow into my veins, and become mine.'
This is an ultimate sacrifice, but the Nightingale accepts and thus she dies.
Unfortunately, the bachelor could not even understand the message that the Nightingale sends right before dying. In a very heartfelt and dramatic moment, the Nightingale asks the student to do something in exchange for her sacrifice:
All that I ask of you in return is that you will be a true lover, for Love is wiser than Philosophy, though she is wise, and mightier than Power, though he is mighty. Flame-coloured are his wings, and coloured like flame is his body. His lips are sweet as honey, and his breath is like frankincense.
Nothing happened. The sacrifice brings no joy, makes no difference, and is-literally- a waste of time. The young woman refused the red rose because it did not go with his dress. The student throws the red rose to a gutter and a cartwheel drives over it. The sacrifice was nothing. The philosophy was nothing. The martyrdom amounted to nothing. There is no fairness in life, nor in love.
The morals are, then:
1. Believing in anything is a choice that comes with the consequences of believing. If you believe in a cause, and are willing to commit to it terminally, then you will have to abide by that.
2. Not two people understand philosophical concepts, nor matters of the heart, in the same way. One cannot expect that the idea of love is the same in any two minds. The Nightingale took a tremendous risk by assuming that the student embraces the same principles as the bird.
3. Everyone gives personal meaning to concepts. The young woman calls the student "rude" for even daring to come near her. He is beneath her station and, as such, he has no business going to meet her. Her definition of rude is as audacious as his definition of "love". No two people name the same thing the same way.
4. Being that there is no fairness in love or life, the takeaway is risk. Either take the risk, or not. There are no winners when there is no risk--there are no losers either. It is entirely the call of each individual.