Albert Barnes Commentary Revelation 21:13

"on the east were three gates; and on the north three gates; and on the south three gates; and on the west three gates." — Revelation 21:13 (ASV)

On the east three gates, etc. The city was square (Revelation 21:16), and the same number of gates is assigned to each quarter. There does not appear to be any special significance in this fact, unless it is to denote that there is access to this city from all quarters of the world, and that those who dwell there will have come from each of the great divisions of the earth; that is, from every land.