What does “the catholic and apostolic Church” mean?

“Also she had a great and high wall” (Rev. 21:12). Who is this wall? The psalmist says, “For you are the God of my strength” (Ps. 43:2). God is the fortress of the heavenly Church and her refuge; we dwell in His secret place and rest under His shadow (Ps. 91:1). This wall gathers the whole community of the catholic Church in a perfect unity that no enemy can infiltrate — neither the devil nor his works can divide her or separate her members.

St. Augustine says, “Blessed is he who lives in the city from which no friend leaves nor enemy invades!” This is the Church, or the catholic city, whose walls gather the whole community of the Church. It is comprised of the Church of both the Old and New Testaments, and it is apostolic — upon its foundations are engraved the names of the apostles of Christ, for he says, “Also she had a great and high wall with twelve gates, and twelve angels at the gates, and names written on them, which are the names of the twelve tribes of the children of Israel: three gates on the east, three gates on the north, three gates on the south, and three gates on the west. Now the wall of the city had twelve foundations, and on them were the names of the twelve apostles of the Lamb” (Rev. 21:12–14). The names of the twelve tribes of Israel, the people of the Old Testament, and the names of the twelve apostles of Christ, the people of the New Testament, have been assembled together, for they are one Church. But those of the Jews who separated themselves from her by rejecting the faith no longer have a place, for the spiritual portion of the inheritance of their tribes has been taken away from them and they have become unbelievers.

The twelve gates symbolize the throwing open of the gates in all directions to all the children of the kingdom.¹³⁶⁶ And the distribution of the gates in the four directions is so that none who desire the eternal inheritance should have difficulty attaining it.