We have considered one structure of the city on high; now we shall consider another. For the city comprises not only the foundation, the gates, the walls, and the streets, but also the assembly of the citizens, who, according to the diversity of their functions, are themselves likewise called foundations, or gates, or walls, or other things of the same kind. And perhaps the name city belongs more properly to a congregation of citizens under the same laws than to a congregation of houses within the same walls. For so Cicero speaks in The Dream of Scipio: The assemblies and gatherings of men united by law are called cities. Of this heavenly city, which consists of citizens, not only St. John speaks in the Apocalypse, but also St. Peter in his first Epistle, and St. Paul in the Epistle to the Ephesians. In the Apocalypse we read that at the twelve gates twelve angels were seen, and names inscribed — the names of the twelve tribes of the children of Israel; while on the twelve foundations were written the names of the twelve apostles of the Lamb (Rev. 21:12-14). In the first Epistle of St. Peter we read: Unto whom coming, as to a living stone, rejected indeed by men, but chosen and made honorable by God, be you also as living stones built up (1 Pet. 2:4-5). In the Epistle to the Ephesians St. Paul writes: Now therefore you are no more strangers and foreigners; but you are fellow citizens with the saints, and the domestics of God, built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone (Eph. 2:19-20). First, then, the city of God has the Apostles and the Prophets for foundations, because the doctrine of the Apostles and Prophets upholds the whole fabric. For faith is the beginning of salvation; and faith was revealed through the Prophets and Apostles: whether concerning the Trinity, the Incarnation, the Resurrection of the dead, the blessed glory, the eternal punishments, or other things that surpass human reason — all these we have learned from the Prophets and Apostles, to whom God deigned to reveal them. But although faith has no place among the blessed, who see what they believed — and what is seen is not believed, but known and beheld — yet the Apostles and Prophets are called the foundations of the city on high, because faith is the beginning of salvation, and thereby the beginning of beatitude. But since St. Peter says that we, as living stones, are built up upon Christ (1 Pet. 2:4-5); and the Apostle Paul himself says in the first Epistle to the Corinthians: For other foundation no man can lay, but that which is laid; which is Christ Jesus (1 Cor. 3:11) — therefore there is one foundation, and there are twelve foundations, as St. Augustine teaches in his exposition of the eighty-sixth Psalm, because Christ was in the twelve Apostles. For He Himself, or His Spirit, spoke and taught through them. Hear the Apostle Paul: Do you seek, he says, a proof of Christ that speaketh in me? (2 Cor. 13:3) Hear Christ Himself: He that heareth you, He says, heareth Me (Luke 10:16). And elsewhere: For it is not you that speak, but the Spirit of your Father that speaketh in you (Matt. 10:20). Nor is there any doubt that the Spirit of the Father and of the Son is one and the same. From which we also understand that in the twelve foundations are understood not only the twelve Apostles, but all those who first preached the same faith; otherwise Paul himself and Barnabas, and the seventy disciples, who were not of the twelve, would not belong to the foundations — nay, the Prophets themselves would not belong to the foundations either, and we should make the Apostle a liar (God forbid), who said that we are built upon the foundation of the Apostles and Prophets.
But a difficulty of no small weight arises: how can Christ be truly called the foundation of the building, since He is the chief cornerstone, as the Apostle says, and has been set as the head of the corner, as the Prophet sings (Ps. 117)? For how can the same stone be at once highest and lowest, in the foundation and at the summit? But if one reflects that these are metaphorical terms, he will understand without difficulty that, on account of different functions, contrary names can belong to one person. Indeed, not only Christ, who is God and man, but every prelate in his church is both foundation and summit: for as foundation he must sustain the weight of the building and bear the infirmities of all, and so be placed beneath all; and yet the same man as summit must be set over all, command all, and be upheld by all. Much more, therefore, will Christ the Lord be able, as the foundation of the Church, to bear all and to sustain all by His authority and power; and at the same time, as set at the head of the corner, to join the two walls and to form one people out of Gentiles and Jews, to preside over all, and to command all.