Closing the gate is meant to be a season-long arc, but the questions that come up in the quest, and the series of reveals and discoveries, are meant to start being the under-pinings for questions, secrets and things that will be explored in future seasons.

Dean [Winchester] is piling on Sam [Winchester], somewhat, for this. What happens is that these brothers start to discover more about what they've done, in the past year, and those tables might turn, in terms of who has to answer for what. I think everybody will get their licks in. No one is going to be a beaten dog for too long.

Closing the gate is meant to be a season-long arc, but the questions that come up in the quest, and the series of reveals and discoveries, are meant to start being the under-pinings for questions, secrets and things that will be explored in future seasons.

Supernatural hasn't spent a lot of time on relationship stories, and this is a really nice mechanism to do that without imposing that on the forward momentum of these other stories that we're telling. In the writers' room we tend to say, "We're never going to be able to give a hell or Purgatory as good as people's imaginations," so the instinct is normally not to go there. But, we went the other way this year and said, "We are going to go there," because there's a really, really strong character thing going on down there.