In that day the branch of the Lord shall be beautiful and glorious, and the fruit of the land shall be the pride and honor of the survivors of Israel. And he who is left in Zion and remains in Jerusalem will be called holy, everyone who has been recorded for life in Jerusalem, when the Lord shall have washed away the filth of the daughters of Zion and cleansed the bloodstains of Jerusalem from its midst by a spirit of judgment and by a spirit of burning. Then the Lord will create over the whole site of Mount Zion and over her assemblies a cloud by day, and smoke and the shining of a flaming fire by night; for over all the glory there will be a canopy. There will be a booth for shade by day from the heat, and for a refuge and a shelter from the storm and rain. (Is. 4:2-6)
With the spector of the horrible judgment in the background, and the shame and disgrace of the Israelite women mentioned (Is. 4:1), Isaiah pours forth words of comfort. The terrible waves of judgment upon the visible Church will be the refining fires upon the Church invisible, the elect of God (Ps. 48:10-11; Zech. 13:9). The remnant of true believers will only be saved in the end (Rom. 9:27, 11:5) and they will prove their faith through going through the same fires as the reprobates within the Visible Church. Whereas the Lord meant the fires for the destruction of the reprobates, they purify the bride of Christ into the pure and spotless bride that she will be. Therefore is it stated that the branch of the Lord, Jesus Christ (Zech. 6:12), shall be beautiful and glorious (v. 2) among the remnant then, and the people of God will be the pride and honor of the land as the bride of Christ.
Now, of course while reading this, we know this is not the case for physical Israel and/or Judah even after the exile, although certainly the worst of the depraved people were wiped out and cut off. Rather therefore, this passage points forward prophetically towards the heavenly Kingdom of our Lord Jesus Christ as it finds its total fulfilment when Jesus comes again. As it can be seen, those who are left in Zion and remains in Jerusalem will not only be called holy (justified) (v. 3), but will be washed away of all their filth and have their sinfulness, symbolized by bloodstains, cleansed away and purged (v. 4); truly made holy. The imagery of verse 5 and 6 also brings back the idea of God's Visible Presence during the times of the Exodus, and thus show forth the actual visible presence and protection of the Lord during that time. All of these verses therefore point forward to the reality of the Second Coming of Christ when God will dwell with His people (Rev. 21:3) who are then totally sanctified in Him.
Therefore, beloved of the Lord, take heart. Though the wrath of God will fall on the earth and cause much distress and destruction as the end approaches, rejoice, for our redemption draws near (Lk. 21:28). This world is a world of tears and sorrow, and we look forward to our heavenly home, where '[God] will wipe away every tear from their eyes and death shall be no more, neither shall there be mourning, nor crying, nor pain anymore, for the former things have passed away' (Rev. 21:4). Amen. Come, Lord Jesus (Rev. 22:20ff).