ARCHETYPES

The castle is the pit because that's were Dauntless is, that's were they keep they're stuff. You have to be "strong" to get in.

The supernatural intervention is Tris being Divergent. She has the ability to do more but has to hide her abilities.

The erudite are the threshold guardians because they are making it hard to Tris to hide that she's divergent.

The Unhealable wound is leaving her family behind because she'll never be able to stop feeling like she betrayed them. 

The water is the serum because it finally shows Tris that she needs to stop hiding that she's divergent she needs to use it to her advantage and save everyone else.