Why do we stone the devil with 49 pebbles during Hajj?

The fundamental principle of stoning the Jamarat is to emulate the Prophet, peace and blessings be upon him. The number of pebbles is seventy if the pilgrim does not hasten. The wisdom behind this number is devotional, meaning it is what the Shari'a has commanded without its rationale being apparent. What is being stoned is the place that Ibrahim, peace be upon him, stoned, not Satan himself, with the intention of vexing him and demonstrating enmity towards him.