for (Christian) marrying, it is essential that I should not be already married with a wife living, sane and undivorced, and so onHe's discussing performatives and how uttering the words 'I do' is an act, not a statement, although certain other conditions are necessary for the words to constitute the act.
At first I read it that Austin himself should be sane and undivorced, but then I thought that it was a bit odd that he should say 'undivorced' - it's fine to be divorced if you want to marry, or not to have been married at all, but undivorced implies married. And being married is a serious stumbling-block to a chap who wants to take a wife.
So I realised that it is the wife that he shouldn't already have who is undivorced (he shouldn't already have a wife who he isn't divorced from). All right, that makes more sense. However, it also means that this hypothetical pre-existing wife should also not be sane if he is to remarry. Also correct, but this implies that if she is insane he is free to marry. Does this mean that if a man's wife (or a woman's husband) is considered to be insane, the marriage is considered void?
I couldn't find any such law with my googling skills, although the search is hampered by the gazillions of websites about how it's insane to get married, the things that drive wives insane, and suchlike. But I don't know US law, and Austin's book is based on his Harvard lectures in 1955, so the law may very well have changed. I did find one article, here, from the worrying-sounding journal Eugenics Review, which from the looks of it is from the early 20th century and gives the legal status of marriage with a 'mentally defective person' (specifically: lunatic, idiot, imbecile, feeble-minded person, or moron) for England and many other countries. Here's what it says about Massachusetts, which is where Harvard is:
We've got off linguistics and onto law now. So to sum up, today we have learnt about performatives and the perils of ambiguous list items. I daresay the Oxford comma fanatics would argue that it would have eliminated the ambiguity.