For, first of all, as eminent, etc.
Note by H Craik to chapter 5 of the Tale of a Tub

The punctuation, which is that of the earliest edition, would seem to shew that for is here a preposition, and not a conjunction, and that the sentence might run, 'First of all, for as eminent a cabalist,' etc. If this is not so, then the first for has caused the omission of a second, which is required by the grammar.