A detailed breakdown of the part in question can be found here
http//www.quran434.com/wife-beating-islam.html#part2
"...guardians/protectors to the unseen/private with what God guarded/protected..." - may be related to what came before, i.e. implying part of being dutiful/obedient is to be this. When used for humans in this way, the unseen (al ghayb) cannot refer to THE unseen, i.e. the same unseen as God knows THE unseen, thus must refer to what is unseen/hidden/private from the people at large and/or her husband, but not to the person addressed. Seems to imply that whatever God ordered to be guarded (i.e. via scripture) in private/unseen, this is what they should guard. Also see 1252 for an example of betrayal in the ghayb/unseen/private.