What does Revelation 21:18 mean?

He who spoke with me had for a measure a golden reed to measure the city, its gates, and its walls.

The city is square, and its length is as great as its width. He measured the city with the reed, twelve thousand twelve stadia. Its length, width, and height are equal.

Its wall is one hundred forty-four cubits, by the measure of a man, that is, of an angel.

The foundations of the city’s wall were adorned with all kinds of precious stones. The first foundation was jasper; the second, sapphire; the third, chalcedony; the fourth, emerald;

the fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, topaz; the tenth, chrysoprasus; the eleventh, jacinth; and the twelfth, amethyst.

The twelve gates were twelve pearls. Each one of the gates was made of one pearl. The street of the city was pure gold, like transparent glass.