Hi simran11, this is a complex text and it is obviously difficult to answer simplistically. I am assuming you would like to know the central symbols Martel employs and why he does so? Here is a start:
Martel uses the symbolism of light and dark imagery throughout the text to highlight the importance of knowledge, literature and wisdom. An example of the association between light imagery and the importance of education can be seen in Pi's response to gaining knowledge from his teachers, "...men and women who came into my dark head and lit a match.." Pi metaphorically compares the gaining of knowledge to the fire emitted from a match strike, thus demonstrating his passion for enlightenment. The "dark head" is an obvious reference to Pi's earlier perceived ignorance. Martel also connects religious enlightenment with light and dark symbolism, through the juxtaposition of beliefs between Mr Kumar and Pi. Mr Kumar associates religion with oppression and ignorance, "Religion is darkness," while Pi believes "Religion is light." So light and dark symbolism is used to demonstrate Martel's concerns of the different ways one may percieve different types of enlightenment; be it spiritual or intellectual.
Martel also uses doors, gates, entrances and exits to symbolise the difference between human, animal and spiritual worlds. Pi's quest for spiritual enlightenment is represented as both a journey and an opportunity through the discovery of the Christian Church, "I noted this, how both the doors were wide open..". The doors are a metaphor for his discovery of Christianity, and also of Pi's movement from being "locked out" or ignorant to spiritual awakening as he "..entered the Church" to gain a new understanding. The gates of the Pondicherry Zoo are also used to symbolise Pi's movement from innocence to knowledge through Pi's father "special lesson" on the dangers of zoo animals. Significantly, Martel highlights the crossing of boundaries from the human world into the world of nature and animals through, "We left the house, went through the gates, entered the zoo."
Additionally, bars, cages and physical boundaries and defined territories are also symbolic of mental and physical landscapes and our desire for security. Martel repeatedly refers to cages and iron bars from the perspective of Pi, his father and the animals, illustrating the concepts of security, protection and territory. This builds on the extended metaphor of the similarities between humans and animals in the way we are forced to behave and choose to behave, ‘All around were great big cages divided up by thick, green, iron bars.’ The earlier "special lesson" Pi witnesses demonstrates that the tiger, like man , has been forced into his situation. He must kill in order to survive, yet hesitates at first to leave the comfort and security of his cage.
I hope this helps:)