Francis Adirumbasamy – also known as Mamaji – is the guru of all gurus. He's the guy who tells the author about Pi. The author describes him in the Nehru street coffee shop as "a spry, bright-eyed elderly man" (Author's Note.1.13). We like Francis. In a way, he's the original spiritual guide of the book. Not only does he direct the author to Pi, he also teaches Pi how to swim—and ability to swim turns into a pretty practical gift when Pi ends up in the middle of the ocean. You could also see it as a metaphor for the gift of faith, which also helps to sustain Pi on the open sea.
If Pi functions more or less as the subject of the novel, Francis is a seed, a catalyst, the spark of the novel. He gives the author the story, and he introduces Pi to spirituality as a practice.
But Mamaji isn't the only figure who teaches Pi. We meet Mr. Kumar the Biology Teacher, Mr. Kumar the Muslim, and Father Martin the Catholic Priest. Each teaches Pi an invaluable lesson. Kumar the biologist shows Pi that science, like religion, is made up of wonder and faith. He's a little cranky and believes science invalidates "the darkness" of religion, but his passion challenges Pi to see science as a committed, atheistic belief, and therefore a type of faith.
Kumar the Muslim teaches Pi to pray. And not just recitation of prayers, but getting the whole body into it, up and down on the prayer mat, until the believer has a connection with God. After Pi leaves Kumar, he says:
"[...] I suddenly felt I was in heaven. [...]. Whereas before the road, the sea, the trees, the air, the sun all spoke differently to me, now they spoke one language of unity. [...]. I felt like the centre of a small circle coinciding with the centre of a much larger one. Atman met Allah." (1.20.5)
If that's not religious ecstasy, please tell us what is.
Each teacher (or teaching), however, seems incomplete. Mr. Kumar the Biologist allows his childhood disease – polio – to erode his faith in God. ("What a terrible disease that must be if it could kill God in a man," Pi says (1.7.17).) In this way, Mr. Kumar allows suffering to diminish his capacity for belief. Perhaps because of this, he exaggerates the power of reason.
Suffering, though, is Father Martin's specialty. He tells Pi about Christ and how the Son of God, because of his love for mankind, must suffer and die just like a human. Father Martin tells Pi how love motivates Christ. In doing so, he shows how human losses and pain can be redeeming. And Mr. Kumar's Sufi Islam seems to actually practice that love through prayer.
All of this is to say these characters contribute practices, ideas, and faiths to Pi. They are their ideas—they serve more as vehicles for viewpoints than characters with deep psychologies. That said, all these ideas find some sort of harmonious existence within Pi. And each completes the other.