Why does Pi use plan seven to keep him alive? What is the significance of the number seven?

In chapter 54, Pi considers the odds of survival while living on a lifeboat with a 450-pound tiger. They aren't good. So, he considers a few options he might have for getting rid of Richard Parker. Pushing him off of the lifeboat first comes to mind; but, with tigers being very good swimmers, he could just swim over and climb back in the boat. Then Pi thinks of attacking him with six morphine syringes, attacking him with all available weaponry, choking...

In chapter 54, Pi considers the odds of survival while living on a lifeboat with a 450-pound tiger. They aren't good. So, he considers a few options he might have for getting rid of Richard Parker. Pushing him off of the lifeboat first comes to mind; but, with tigers being very good swimmers, he could just swim over and climb back in the boat. Then Pi thinks of attacking him with six morphine syringes, attacking him with all available weaponry, choking him with rope, poisoning him, setting him on fire, and electrocuting him. These ideas are flawed because of the lack of materials or because of uncertain outcomes. Plan number six is simply to outlast the tiger with patience and hope the tiger dies first; but this is passive, and not proactive. It isn't until chapter 57 that Pi gets the seventh idea to tame the tiger.

Taming the tiger becomes the most productive, proactive and efficient idea because it helps Pi to establish himself as a predator rather than prey. Plan number seven also helps Pi to claim more territory on the boat, and it enables him to provide food and water for Richard Parker more easily. Providing food for the tiger forces it to become dependent on Pi for its needs. Pi thus solidifies his importance on the boat, which should hold off the tiger from eating him.

The number seven is significant because of the ties it has to the Bible and Christianity—one of the religions Pi believes in. For example, the Bible says that God created the world in six days and rested on the seventh; Jacob, whose name is later changed to Israel, works seven years in order to marry Rachel; Jericho is taken after seven days of laying siege to it; there are seven seals, seven vials, seven churches; and the list goes on. The number seven is evidently sacred.