“The Things We Left Behind” touches on serious themes as Supernatural reaches its mid-season finale. The undercurrent of this episode lies in how our families shape who we are. Though the importance of family in determining who we are and what we choose to do is one of the main themes of Supernatural generally, this episode takes it further by exploring how personal choices affect members of our family. We begin to see reflection on the consequences of actions taken by Castiel and Dean. Rowena’s impact on Crowley and the legacy it has borne starts to become more evident as well. There are things that our characters may have thought, or hoped, they had left behind, but this episode reveals what they still carry with them and what might not be so easily forgotten.