Thucydides, the ancient Greek historian and writer once said that the secret of happiness is freedom. The nightingale is a free bird flying freely over the trees lakes rice fields etc. This makes him happy and he sings charming songs of joy. Even when he visits the palace to sing for the princess he has the freedom to fly in and out at his own sweet will.
However when the princess puts him in a cage the bird becomes sad and he simply cannot sing. Human nature is quite complicated and often difficult to understand. It is a natural human tendency to possess something that one likes. Princess September dwells upon this very psychology of human nature.
The princess becomes so fond of the nightingale and his voice that she wants to possess him for herself. The elder princesses tell her to put the bird in a cage as he would be safer inside. Moreover this way Princess September would also be assured that the bird would never leave her. Nature is always seen to have a beneficial effect on living creatures.
The nightingale sings best in the lap of nature. When the princess shuts him inside a cage, he simply refuses to sing, saying that he wants to see the trees and the lake and the green rice growing in the fields. It is these beauties of nature which inspire the nightingale to sing beautiful songs.
The influence of nature is seen in the life of Princess September. After she grants the bird freedom, she keeps the window of her room open day and night, so that the little bird might come into the room whenever he feels to do so.
This proved to be favourable for her.
With the windows open, natural air and sunshine got into the room. The Princess got Nature's nourishment which enhanced her beauty. Thus, the princess grew up to be extremely beautiful. The other eight princesses never slept with the windows of their room open. Naturally no fresh air or light entered the room. Lacking in nature's nourishment, they grew up to be ugly and unpleasant.
While on the one hand, the story speaks of the cordial relationship between humans and animals, as the friendship between Princess September and the nightingale; on the other hand, it also conveys the message of preventing cruelty to animals.
Taming animals for the sake of one's hobby or as a status symbol, often proves to be quite cruel to the dumb creatures. Instead of putting the animals or birds in a cage, or tying them with metal chains, we must let them move around freely. What we feel to be an expression of our love for them sometimes infringes on their freedom and may become destructive or fatal.