When a spy kills someone very close to them to deceive their darkoverlord into believing that they are the ultimate agent. (When Snape kills Dumbledore)
The agent we sent was assigned to snape-kill a loved one in order to overthrow the enemy.
Killing someone to deceive your dark overlord into believing that you are their ultimate agent.
(Snape killed Dumbledore to deceive Lord Voldemort into believing Snape was his ultimate agent)
Kylo Ren needed to prove his worth to Snoke because Kylo is actually getting back at the dark side for killing his loved one, as seen by the possible grave Luke stands next to at the end of "The Force Awakens", so he Snape killed Han Solo. (This is JUST a THEORY) kylo ren severous snape dumbledore voldemort snape killing