211 Pearls are produced by oysters in the waters of death. When an oyster is wounded by a grain of sand, it secretes its life-juice around the grain of sand and makes it into a precious pearl. This depicts Christ as the living One coming into the death waters, being wounded by us, and secreting His life over us to make us into precious pearls for the building of God's eternal expression. That the twelve gates of the holy city are twelve pearls signifies that regeneration through the death-overcoming and life-secreting Christ is the entrance into the city. This meets the requirement of the law, which is represented by Israel and is under the observing of the guarding angels (v. 12).
The New Jerusalem is built of three kinds of precious materials, signifying that she is built with the Triune God. First, the city proper, with its street, is of pure gold (vv. 18, 21). Gold, the symbol of the divine nature of God, signifies the Father as the source, from whom the element for the substantial existence of the city is produced. Second, the twelve gates of the city are pearls, which signify the Son's overcoming death and life-imparting resurrection, through which entrance to the city is gained. Third, the wall of the city and its foundation are built of precious stones, signifying the Spirit's work of transforming the redeemed and regenerated saints into precious stones for the building of God's eternal habitation that they may express God corporately in His all-permeating glory. In the garden of Eden these three kinds of treasures merely existed as materials (Gen. 2:11-12), whereas in the city of New Jerusalem these precious materials become a builded city for the fulfillment of God's eternal purpose, which is to have a corporate expression.