why did pi choose to practice 3 religions?

Answer 1

Religion can help people comprehend and find "meaning". We learn about many religions and take in for ourselves the "meanings" only that we learn from people whom we RESPECT among our elders, loved-ones, teachers, clergy and philosophers. When we respect people with different religions, for example a Confucian grandfather and a Catholic mother and a Shinto sister-in-law, we are then open to learn their "meanings" and to practice all three faiths.

Answer 2

i hope your talking about "the life of pi."
Anyway, Pi was a Hindu because his family was; this was the religion in which he was raised. He could not drop this religion. Then he picked up Islam and Christianity because they were both so appealing in their own way. Christianity intrieged him because of the fact that Christ died. Gods were supposed to be invulnerable (like Krishna) but if Christ died for mankind and still maintained his immortality, then he is someone to be praised. He practiced Islam because he was amazed by the faith and strength of the Muslims. Their religion was so rigorous and their meditations so fullfilling. He also loved his Muslim teacher, who was so hidden and hard to see (almost invisible). The teacher showed him the muslim method of meditiation and Pi was fascinated.
This passage really answered the question for me:
“‘I don’t see why I can’t be all three. Mamaji has two passports. He’s Indian and French. Why can’t I be a Hindu, a Christian and a Muslim.’
‘That’s different. France and India are nations on earth.’
‘How many nations are there in the sky?’
She thought for a second. ‘One. That’s the point. One nation, one passport.’
‘One nation in the sky?’
‘Yes. Or none. There’s that option too, you know. These are terribly old-fashioned things you’ve taken to.’
‘If there’s only one nation in the sky, shouldn’t all passports be valid for it.’” (Ch. 26, p. 74)