You won't find a more apt example of an excerpt that is contradictory to an author's broader writings than this bit from C.S. Lewis' Mere Christianity:
Before leaving the question of divorce, I should like to distinguish two things which are very often confused. The Christian conception of marriage is one: the other is quite the different question—how far Christians, if they are voters or Members of Parliament, ought to try to force their views of marriage on the rest of the community by embodying them in the divorce laws. A great many people seem to think that if you are a Christian yourself you should try to make divorce difficult for every one. I do not think that. At least I know I should be very angry if the Mohammedans tried to prevent the rest of us from drinking wine. My own view is that the Churches should frankly recognize that the majority of the British people are not Christian and, therefore, cannot be expected to live Christian lives. There ought to be two distinct kinds of marriage: one governed by the State with rules enforced on all citizens, the other governed by the church with rules enforced by her on her own members. The distinction ought to be quite sharp, so that a man knows which couples are married in a Christian sense and which are not.
This argument provoked a strong response from Lewis' friend and fellow Inkling, J.R.R. Tolkien. Tolkien drafted a response to Lewis sometime in 1943 but never sent it. After Tolkien died, the letter was found folded up inside his copy of Lewis' "Christian Behavior,"which would be republished as part of Mere Christianity. (I've added the emphasis.)
My dear L.,
I have been reading your booklet 'Christian Behavior." I have never felt happy about your view of Christian "policy" with regard to divorce. …
[Y]ou observe that you are really committed (with the Christian Church as a whole) to the view that Christian marriage—monogamous, permanent, rigidly "faithful"—is in fact the truth about sexual behavior for all humanity: this is the only road of total health (including sex in its proper place) for all men and women. That it is dissonant with men's present sex-psychology does not disprove this, as you see: "I think it is the instinct that has gone wrong," you say. Indeed if this were not so, it would be an intolerable injustice to impose permanent monogamy even on Christians. If Christian marriage were in the last analysis "unnatural" (of the same type as say the prohibition of flesh-meat in certain monastic rules) it could only be imposed on a special "chastity-order" of the Church, not on the universal Church. No item of compulsory Christian morals is valid only for Christians. … I do not think you can possibly support your "policy," by this argument, for by it you are giving away the very foundation of Christian marriage. The foundation is that this is the correct way of "running the human machine." Your argument reduces it merely to a way of (perhaps?) getting an extra mileage out of a few selected machines.
The horror of the Christians with whom you disagree (the great majority of all practicing Christians) at legal divorce is in the ultimate analysis precisely that: horror at seeing good machines ruined by misuse. I could that, if you ever get a chance of alterations, you would make the point clear. Toleration of divorce—if a Christian does tolerate it—is toleration of a human abuse, which it requires special local and temporary circumstances to justify (as does the toleration of usury)—if indeed either divorce or genuine usury should be tolerated at all, as a matter of expedient policy.