"It" is the new Jerusalem, the Wife of the Lamb. The "nations of them that are saved" consist of people who are saved but who are not part of the Church.

Some of the members of the churches of today are serving as a firstfruits of the entire Wife of the Lamb. They are a bride within the larger Bride, so to speak. They reveal in themselves what one day will be true of the entire Church, the Wife of the Lamb. They are pressing forward in Christ. They are washing their robes in the blood of the Lamb until they are spotless in righteousness, holiness, and obedience to God.

They now are attaining what one day must be true of every member of the Body of Christ.

That he might present it to himself a glorious church, not having spot, or wrinkle, or any such thing; but that it should be holy and without blemish. (Ephesians 5:27)

The ministries that have come to us from the ascended Jesus will continue to operate until the whole Church, not just the firstfruits, has been brought to perfection.

Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ: (Ephesians 4:13)

But what is true of the churches of today, the golden Lampstands of God?

But I have a few things against thee, because thou hast there them that hold the doctrine of Balaam, who taught Balac to cast a stumblingblock before the children of Israel, to eat things sacrificed unto idols, and to commit fornication. (Revelation 2:14)

Notwithstanding I have a few things against thee, because thou sufferest that woman Jezebel, which calleth herself a prophetess, to teach and to seduce my servants to commit fornication, and to eat things sacrificed unto idols. (Revelation 2:20)

Behold, I will cast her into a bed, and them that commit adultery with her into great tribulation, except they repent of their deeds. And I will kill her children with death; and all the churches shall know that I am he which searcheth the reins and hearts: and I will give unto every one of you according to your works. (Revelation 2:22,23)

In the above passages, Christ is addressing the churches on the earth. The contrast between the description of the Lord's beloved that is found in the Song of Solomon, and the rebuke of Christ directed toward the seven churches of Asia, leads to but one conclusion: there is a firstfruits of the Church, of the Wife of the Lamb, that consists of the victorious saints; of those who will walk with Christ in white because they have been found to be worthy.

This agrees with the concept found in Song of Solomon 8:10:

I am a wall [have overcome the enemy], and my breasts like towers [have borne much fruit, thereby gaining dominion]: then was I in his eyes as one that found favour.

To be continued.