Ever since the beginning of this season, when Lucifer (TOM ELLIS) awoke in the desert to find his wings had grown back, he's been raising Cain about it.
But Cain says he had nothing to do with it.
That's right, the literal biblical Cain, the world's first murderer, is immortal because of the mark God placed upon him that no man could touch him. You might recognize him by his current identity, Lt. Marcus Pierce (TOM WELLING). Yes, he did arrange for Lucifer to be kidnapped and dragged away to the desert, but only to get him out of the way so that Cain could get close to Chloe (LAUREN GERMAN) to achieve his ultimate goal: to die.
Which means God gave Lucifer his wings back to interfere in Cain's plan, and they've both been pawns of the Almighty.