^^ That's what I was thinking, too. "Locking the gates" is always discussed in the context of keeping things in, not out. It would be nice if they were more explicit about that, though, especially since Metatron hinted that locking the gates may not have entirely desirable consequences.
And, speaking of Metatron, he's undergone quite a change in attitude-- he's gone from being a heavenly hermit to wanting to take over. How much do you want to bet that Sam and Cass finish their respective trials at the same time?
I can't wait to see them try to cure Crowley. That ought to be good.