Albert Barnes Commentary Revelation 21:12

"having a wall great and high; having twelve gates, and at the gates twelve angels; and names written thereon, which are [the names] of the twelve tribes of the children of Israel:" — Revelation 21:12 (ASV)

And had a wall great and high. Ancient cities were always surrounded with walls for protection, and John represents this as enclosed in the usual manner. The word great means that it was thick and strong. Its height also is particularly noticed, for it was unusual. .

And had twelve gates. Three on each side. The number of the gates corresponds to the number of the tribes of the children of Israel, and to the number of the apostles. The idea seems to be that there would be ample opportunity of access and egress.

And at the gates twelve angels. Stationed there as guards to the New Jerusalem. Their business seems to have been to watch the gates that nothing improper should enter; that the great enemy should not make an insidious approach to this city as he did to the earthly Paradise.

And names written thereon. On the gates.

Which are the names of the twelve tribes of the children of Israel. So in the city which Ezekiel saw in vision, which John also seems to have had in mind. . The inscription in Ezekiel denoted that it was the residence of the people of God; and the same idea is denoted here. The New Jerusalem is the eternal residence of the children of God, and this is indicated at every gate. None can enter who do not belong to that people; all who are within are understood to be of their number.