GK Chesterton Responds to Pope Francis

This is from The Everlasting Man.  My emphases of his text in boldface; my comments in italics.  He is speaking here on the view of Marriage as presented by Our Lord (see Mat. 19)

What he [Jesus] advanced
was something quite different; something very difficult; but something
no more difficult now than it was then. When, for instance, Mahomet made
his polygamous compromise we may reasonably say that it was conditioned
by a polygamous society. When he allowed a man four wives he was really
doing something suited to the circumstances, which might have been less
suited to other circumstances. Nobody will pretend that the four wives
were like the four winds, something seemingly a part of the order of
nature; nobody will say that the figure four was written for ever in
stars upon the sky.

[Chesterton is implying here that Christ is asserting that the nature of Christian Marriage is "part of the order of nature", a fidelity that is somehow "for ever written in the stars upon the sky" in the way no worldly compromise could be.

But neither will anyone say that the figure four is
an inconceivable ideal; that it is beyond the power of the mind of man
to count up to four; or to count the number of his wives and see whether
it amounts to four.

[Chesterton is using humor here to illustrate a point.  "The Islamic view of Marriage is an impossible ideal for me!  How on earth am I to count my wives and assure myself that I have only four?  It can't be done!"]

It is a practical compromise carrying with it the
character of a particular society.

[This is Chesterton's point.  Mohammed's compromise on marriage was a compromise with the Middle Eastern pagan society and culture of his day.  Christ's teaching on Marriage - and therefore the Church's - is no compromise at all, and certainly not a compromise with the world or the world's "compromised" attitude toward love, matrimony and fidelity.]  

If Mahomet had been born in Acton in
the nineteenth century, we may well doubt whether he would instantly
have filled that suburb with harems of four wives apiece. As he was born
in Arabia in the sixth century, he did in his conjugal arrangements
suggest the conditions of Arabia in the sixth century. But Christ in his
view of marriage does not in the least suggest the conditions of
Palestine of the first century. He does not suggest anything at all,
except the sacramental view of marriage as developed long afterwards by
the Catholic Church.

[Christ taught something in the Gospels that was only fully expressed later.  His teaching on Marriage is radically unworldly and new, and not the least conditioned by the world around him - either the Roman attitude toward Marriage or the Jewish.  It was a new thing, a suddenly and startlingly right thing - and insisting on it was one of the reasons people were furious with Him.] 

It was quite as difficult for people then as for
people now. It was much more puzzling to people then than to people now.
Jews and Romans and Greeks did not believe, and did not even understand
enough to disbelieve, the mystical idea that the man and the woman had
become one sacramental substance. 

[It is this central teaching of Jesus on Marriage that the Catholic Church has always defended, with true mercy and not a parody of mercy - mercy for those abandoned by their spouses and mercy for the broken children of broken families, as well as mercy for those who do the breaking and who repent of it.  The worldly pressure to compromise or abandon this teaching today is enormous and it has infested the Church at every level.  But of all the Catholic doctrines based on the teachings of Christ, this is perhaps the one with the most Scriptural support.  When it comes to Marriage, Pope Francis in his apostolic exhortation and elsewhere refuses to clarify; Jesus in the Gospel refuses to be vague.  If the Catholic Church folds on "the mystical idea that the man and the woman become one sacramental substance", or that rejecting this idea by an ongoing sin throws the sinner out of full communion with Christ, the Church will have folded indeed. If the Bride of Christ abandons Marriage she will have abandoned the bridegroom Himself.] 

We may think it an incredible or
impossible ideal; but we cannot think it any more incredible or
impossible than they would have thought it. In other words, whatever
else is true, it is not true that the controversy has been altered by
time. Whatever else is true, it is emphatically not true that the ideas
of Jesus of Nazareth were suitable to his time, but are no longer
suitable to our time. Exactly how suitable they were to his time is
perhaps suggested in the end of his story.