Hi Marie. That's a good question. In this context, "for" is a slightly more old-fashioned and uncommon way of expressing justification. It can be compared to "since" or "because". For example:
"She wasn't hired for the job, for she didn't have enough experience."
The following sentences convey exactly the same meaning:
"She wasn't hired for the job because she didn't have enough experience."
"She wasn't hired for the job, since she didn't have enough experience."
Please let me know if you have any further questions.
Kind regards,
Josh