Here's a link to Holy Willie's Prayer, and also to its sequel Holy Willie's Epitaph.

I can't see that there's anything out-of-line in pointing a contradiction between sounding off too loudly about the overriding importance of the institution of marriage, and yet being somewhat flexible about it in private life.

It's the kind of thing that was just up Holy Willie's street. The point being, when we expect other people to accept our own failings, we should be willing to accept theirs as well.