And I saw the HOLY CITY, NEW JERUSALEM,
From the previous verse, we can imply that this is a NEW kind of JERUSALEM from the NEW HEAVEN. The term, HOLY CITY, denotes that it will be the center of spirituality. In the previous earth, JERUSALEM also was referred to as the HOLY CITY, but it had one thing wrong with it. It was tainted by evil. It was where prophets were murdered (Luke 13:31-34-35), it was where Jesus Christ was crucified (Luke 23:26-28-31), and it was where the two witnesses were killed (Revelation 11:8).
This is the place where believers are housed eternally forever (Hebrews 12:18-22-29). What distinguished this NEW JERUSALEM is that John saw it
coming down out of HEAVEN from GOD,
This HOLY CITY is pure and righteous. In fact, it is pure enough for God Himself to live in (next verse). This HOLY CITY was the place Abraham by faith was looking for (Hebrews 11:8-10-16-22). And this HOLY CITY is
made ready as a bride adorned for her husband.
This is Dad's wedding gift to His son. We studied about the marriage supper (Revelation 19:1-10), and now this is the permanent address for the HOLY Couple. Much of the rest of this chapter (verses 9-27) will describe Dad's gift in more detail.