The symbolism of the sheep can best be understood if we first recall some of the lyrics found in the oratoria Messiah composed by the great George Frideric Handel:
All we like sheep have gone astray-ay-ay-ay-ay-ay-ay-ay-ay-ay. We have turn-ed, we have turn-ed everyone to his own way; everyone to his own way.
Translation: "All we like sheep have gone astray. We have turned everyone to his own way."
While Saint-Exupery may not exactly have had Handel in mind when he wrote both the opening chapters and the ending to the Little Prince, he certainly did have biblical allegory in mind. Biblical allusions can be seen all throughout the book. The snake that kills the prince is the same biblical serpent that symbolizes death in the Garden of Eden. It has also been noted that the pilot is lost in the desert just as the Israelites were lost in the desert coming out of Egypt. In addition, in the 25th chapter, both the pilot and the prince go in search of water and find a well unlike the wells in the Sahara that are "mere holes dug in the sand" but instead "like a well in a village," which is symbolic of Christ's well in Samaria and living water (eNotes, "Literary Precedents"). Finally, the prince experiences a transcendence. Not only does he die to reach a higher plane but also experiences a sort of resurrection as his body is not found at sunrise the next day, symbolic of Christ's transcendence and resurrection.
Hence, the sheep the prince asks the pilot to draw in the very beginning of the story is also a biblical allusion. We must remember that at the moment the pilot meets the prince, the prince has returned to the desert in order to make his way back home, a home that the prince ran away from a year ago. Feeling lost, confused, and rejected by his flower, the prince left his home to try and gain new understanding. He went astray. He ran from the one thing that was important to him, love. And now like a sheep returning to the fold, he realizes that he has acted as a sheep and gone astray; therefore, he is asking the pilot for a drawing of a sheep to forever remind him of the journey he has had as a lost sheep and to remind him of his spiritual transformation.
It becomes evident that the sheep is not only symbolizing spiritual floundering but also spiritual transcendence when the prince dies. Like the Lamb of God, the prince must experience death to be returned to his point of origin. The symbolism of the prince as the Lamb of God is also evident earlier when the prince first meets the snake who calls the prince "innocent and true" (Ch. 17).
Hence we see that the snake symbolizes both spiritual floundering and spiritual transcendence and that the prince is meant to represent the Lamb of God.
In the beginning, the sheep is simply another source of curiosity for the little prince. He was aware of the existence of sheep and wanted to learn more about them. In his openness to knowledge and his willingness to see and understand with his imagination, the "very small sheep" in the box is a perfect outlet for his creative love.
The pilot comes to understand that the sheep, much as the little prince loves him, represents a threat to another beloved possession of the prince's - his rose. The prince is horrified to realize that the sheep might eat the rose, just as it eats grass and small bushes.
If some one loves a flower...He can say to himself, 'Somewhere, my flower is there...' But if the sheep eats the flower, in one moment all his stars will be darkened...
The sheep represents the dual nature of true love and of great commitment. In giving ones devotion to anything, one receives great pleasure and reward but also takes the risk of being deeply saddened or hurt.