From the Commentary of St Augustine, Bishop on Psalm 86 [on the Feast Day of St Matthias, Apostle – May 14]
“The foundations thereof are in the holy mountains; the Lord loves the gates of Sion” [Ps 86:1]. Why are the apostles and prophets called foundations? Because their authority bears up our weakness. Why are they called gates? Because through them we enter the kingdom of God. For they preach to us, and when we enter through them, we enter through Christ; for he is the gate.
And whereas it is written that Jerusalem has twelve gates, Christ is the one gate and Christ is also the twelve gates; and, therefore, the apostles are twelve in number. There is a great mystery in the signification of this number twelve. “You shall sit,” says our Lord, “upon twelve thrones, judging the twelve tribes of Israel.”
The twelve gates
But there are twelve thrones there, there is no throne for Paul, the thirteenth Apostle, to take his seat and judge; and yet he said that he was to judge not only men but angels. Which angels, unless the fallen angels? “Know you not,” he says, “that we shall judge angels?” The multitude might answer him: “Why do you boast that you are about to judge? Where is your throne? The Lord said that there were to be twelve thrones for the twelve Apostles. One – Judas – fell indeed, but holy Matthias was appointed in his place; and so the number of twelve thrones was filled up. First find the place where you shall sit, and then threaten that you will judge.”
Let us, therefore, consider what these twelve thrones mean. The mysterious term signifies a sort of universality; for the Church was spread through all the earth, whence this edifice is styled a building-together to Christ.
The twelve thrones
And therefore, there are twelve thrones, since mankind comes from all quarters to be judged; and in like manner there are twelve gates to the heavenly city, because mankind will come from all quarters to enter it.
So, not only the Twelve and the Apostle Paul, but all who are to judge, will have part in these twelve thrones, according to this notion of universality; even as all who enter, must enter by one or other of the twelve gates.
For the four quarters of the earth, East, West, North and South, are constantly mentioned in the Scriptures.
From all those four winds, the Lord declares in the Gospel, he will gather his elect; therefore, from all those four winds is the Church called. But how is it to be called? On every side, it is called in the name of the Trinity. Not otherwise is it called than by baptism in the name of the Father, and the Son, and the Holy Spirit. Therefore, four being taken thrice, the number twelve is found.
– From: An Approved English Translation of the Breviarium Romanum, Burnes & Oates, London, 1964