Creation of a Gem - You!

Usually, when a young man prepares himself to ask his girlfriend to marry him, he offers her a diamond engagement ring. Not often does the lucky lady ask what mine this diamond came from. Our earth houses a lot of stones that are embedded in rock several miles below the earth's surface. Millions of years in the making and waiting for the exact time and pressure to build up to present themselves to the world. In the book of Revelation chapter 22, mentions 12 stones that are carefully crafted as a foundation of the wall of the New Jerusalem. Of all the stones God has created, why did he choose these 12 stones? Why are they the chosen few?