The meaning of "for strength should avail me"

There is a thought that for strength should avail me, Though both of shelter and kindred despoiled; Heaven is a home, and a rest will not fail me; God is a friend to the poor orphan child."

The passage above is sung by Bessie, one of the maids at Gateshead in Jane Eyre by Charlotte Bronte.

I can not figure out what the underlined ‘for’ is for. In grammatical sense ‘for strength’ is put in subject’s position.

But it doesn’t seem to be a subject in form.

(Am I right, so far?)

And last and foremost it doesn’t make any sense to me.

I can’t figure the line’s exact meaning.

Thanks in advance.