"for" meaning?

HI! everyone.
Could you tell me what purpose does "for" serve in the sentence below?
And also what does "socially prescribed" mean here?
The preoccupation with socially advantageous marriage in nineteenth-century English society manifests itself here, for in claiming that a single man “must be in want of a wife,” the narrator reveals that the reverse is also true: a single woman, whose socially prescribed options are quite limited, is in (perhaps desperate) want of a husband.
Thanks!