As a “mysticum vocabulum”1, Babylon...expresses the nature of [the earthly] city, for it signifies confusio: confusion, diversity, division; thus the counterpart to unitas, by means of which being one is reached, the fullness of being. From here it is made clear why the civitas terrena is not a united group, but presents itself rather as a multitude of cities necessarily in inner-strife: precisely because she is confusio. At the same time the contrary image arises at this point: the unitas, that is, the catholic Church.2
1. Unitas
1 Civ [De Civitate Dei] XVIII 41,2 (601); cf XVI 4 (482) and passim.
With this affirmation we have gone beyond the historical boundaries of the earthly city, penetrating into the definition of its essence. It presents itself as a city of disunity. And this not only on the level of political life, but likewise and greatly in the spiritual life. The wisdom of the world is characterized by the dissensiones philosophorum, in contrast with the concordia scripturarum on the part of the divine wisdom of the Church3. Here, at the same time, another aspect is made clear: fundamental error does not exclude relative goodness. The philosophers in great numbers have come to know decisive and important truths4; nevertheless, philosophy taken as whole is insufficient—for it belongs to the civitas terrena, since it fails in the decisive question: that regarding beatitudo5, which is at issue in the entire dispute—.
2. Justitia and utilitas
We come yet one step closer to the essence of the earthly city if we begin with the definition of a people given by Cicero: “Populum […] coetum iuris consensu et utilitatis communione sociatum esse determinat”6. Augustine thinks that the application of this definition would have to deny the earthly people the character of a people, and, with that, to the city the character of a city7. For both of the essential elements are missing from the earthly city, the unity in law and the communion in “utility”. The unity in law: since law (right) can only be had where there is justice. And there is justice only where the body is subordinated to the spirit and the spirit is subordinated to God. But servire Deo is missing with total evidence from the pagan cities, and with that also iustitia, and with that juridical unity8. But a true utility is likewise also missing in that association. Since by utility what is meant is the fundamental desire of man: the desire for happiness. This is in fact the dominant desire of the city: but it seeks happiness by erroneous ways: by serving the gods. In reality, nevertheless, as we said before: happiness can only be had by serving the one God. In other words: the communio unitatis is only possible in a communion which is simultaneously communio in the true veneration of God9.
1 Civ [De Civitate Dei] XVIII 41,2 (601); cf XVI 4 (482) and passim.
2 On the “unitas” of Babylon cf. also En in Ps [Enarrationes in Psalmos] 61,15 (PL 36,740): “etsi de opinionum varietate in diversum, de vanitate tamen in unum sunt”. Likewise in En in Ps 80,14 (PL 37,1040).
3 Civ XVIII 41: see the title of the chapter (PL 41,600).
4 Ibid., 41,3 (602). The creation of the world is mentioned among the truths discovered by the philosophers.
5 Civ XVIII 41,3. Just as much here as in his first writings Augustine sees the indication of the way to beatitudo as the decisive mission of philosophy, without limiting itself to shedding light on knowledges.
6 Civ II 21,2 (67).
7 Civ XIX 21 (648-650); 23,5 (654s).
8 Ibid., 21,2 (649).
9 Ibid.: “Quamvis enim si diligenter attendas nec utlitas sit ulla viventium, qui vivunt impie, sicut vivit omnis, qui non servit Deo vervitque daemonibus” On the concept of pietas, cf. infra. Likewise, further on, on the civitas Dei and Church.
Joseph Ratzinger, 1951 Thesis on Augustine in Obras Completas I, 2014, 313-314, and Gesammelte Schriften, 2011, 372-374. --Plinthos translation.