Jamieson, Fausset and Brown on Revelation 21:12

12. And--A and B omit. Eze 48:30-35, has a similar description, which implies that the millennial Jerusalem shall have its exact antitype in the heavenly Jerusalem which shall descend on the finally regenerated earth.

wall great and high--setting forth the security of the Church. Also, the exclusion of the ungodly.

twelve angels--guards of the twelve gates: an additional emblem of perfect security, while the gates being never shut (Re 21:25) imply perfect liberty and peace. Also, angels shall be the brethren of the heavenly citizens.

names of ... twelve tribes--The inscription of the names on the gates implies that none but the spiritual Israel, God's elect, shall enter the heavenly city. As the millennium wherein literal Israel in the flesh shall be the mother Church, is the antitype to the Old Testament earthly theocracy in the Holy Land, so the heavenly new Jerusalem is the consummation antitypical to the spiritual Israel, the elect Church of Jews and Gentiles being now gathered out: as the spiritual Israel now is an advance upon the previous literal and carnal Israel, so the heavenly Jerusalem shall be much in advance of the millennial Jerusalem.