In the end, Kiriel heads back to his world while Shaun gets another shot at life. This time around, though, Shaun gets to survive being run over. Sure, he'll be in a lot of pain and in a coma for a while, but at least he gets to live.
Why is this so important? Kiriel wants to have an impact on someone. He thinks his whole life is wasted down below, watching other people suffer, so while he's above ground, he thinks about leaving his mark on the world. Luckily, he gets just that with Shaun. The guy gets to live another day because of Kiriel. Yep, that's some impact.