There are three important characteristics of civilization mentioned here: (a) a tacit agreement or norm; (b) fundamental (even if minimal) equality; (c) a taboo against causing or facilitating others to lose face. Losing face produces both (d) loss of respect for the person principally concerned among others and (d) embarrassment or (or depending on the culture) shame in the person principally concerned. (In context, Coetzee's narrator, who is 'Coetzee,' accepts Japan as an obvious site for such a norm, but recognizes that England may have it, too.)
As an aside, this understanding of civilization is one of the transformative by-products of the youthful's Coetzee struggle with loneliness, his inability to produce art and sexual coldness, and his recognition of his own misanthropy, not to say, being a bastard (especially to women). Earlier in the (auto-biographical) novel, Coetzee had accepted other understandings of civilization including (i) an elitist "Anglo-French" conception centered on rare, particular literary cultural products exemplified by Athens, Rome, the "Germany of Walther von der Vogelweide, Provence of Arnaut Daniel, the Florence of Dante and Guido Caculcanti, to say nothing of Tang China and Moghul India and Almoravid Spain" (pp. 24-26) on the authority of the philanthropic Pound T.S. Eliot; (ii) a political conception centered on Christian values and history of colonial settlement in Southern Africa (p. 38-9) on the authority of self-interested and partial politicians.
It would be reductive to see in Coetzee's tripartite understanding of civilization merely a coordination problem among unequal members of a society --- England's classes, South Africa's racial and linguistic communities, etc. -- who struggle to find a thin, abstract layer of mutual, equal respect. For, preventing the loss in face in others requires judgment and tact. General rules can guide us in preventing us from generating circumstances in which these may be necessary and can, even, (Adam Smith is very good on this) help us feel what we ought to feel absent any feeling at all (or correct against self-deception). But general rules cannot teach us the skills and tenor of character needed to navigate social nuance. (Perhaps, deep learning will solve this problem, but I am skeptical.) Coetzee's narrative suggests that individuals, even whole cultures, can achieve adulthood without ever mastering the skill.
I often Digress about civility (see here) and civilization (see here). At one point (here) I had suggested that civilization is no more than the art of keeping conversation going; and that philosophy's role in civilization is to teach the skills and develop the concepts that allow conversations to be continued or, alternatively, the state of war to be held at bay. At first sight Coetzee's and my approach have little overlap. But it's not too difficult to see that Coetzee's analysis of civilization can be treated as a means to achieving what I have been calling civilization. This, then, results in civilization being, (a) a tacit agreement or norm; which presupposes (b) a fundamental (even if minimal) equality among members of a society;* in which there is (c) a taboo against causing or facilitating others to lose face in order (d) to keep the conversation, including silences and long-stutters, going.
Professional philosophy today is pretty good at fleshing out and analyzing (a-b). And I believe it is even capable of teaching the skills and concepts necessary for these. As I often document (and as Eric Schwitzgebel, Michael Rea, and Amy Olberding have also emphasized in various ways), professional philosophy today is horrid at (c-d)--that is we often instantiate uncivilized behavior (in the sense discussed here) and we probably lack the skills to teach it to others. That is to say, we may, in fact, at the margin contribute to the decline of society's inability to keep conversation going.