Isaiah 4, A Beautiful Branch

The judgment of the wealthy women of Zion began in chapter 3. 

Isaiah 4: 1, Desperate women

In that day seven women

    will take hold of one man

and say, “We will eat our own food

    and provide our own clothes;

only let us be called by your name.

    Take away our disgrace!”

This is a continuation of the previous chapter, a description of the despair of the women of Israel in that coming day. In that coming day, says God, the women promise to pay for all their needs but beg for a man to take away their disgrace. (Presumably the metaphor suggests the disgrace of being mothers of illegitimate children, mothers without a husband?)

Isaiah 4:2-4, Branch of the Lord

In that day the Branch of the Lord will be beautiful and glorious, and the fruit of the land will be the pride and glory of the survivors in Israel. 

Those who are left in Zion, who remain in Jerusalem, will be called holy, all who are recorded among the living in Jerusalem. The Lord will wash away the filth of the women of Zion; he will cleanse the bloodstains from Jerusalem by a spirit of judgment and a spirit of fire. 

The mood of the passage turns -- now we have a branch of God, a branch of Israel, saved and protected, cleaned up and honored. As Grogan points out, the term "branch" (here tsemach) takes on a significant Messianic meaning in Isaiah (see 11:1 where a different word, netser, is used) and in the prophetic books of Jeremiah and Zechariah (Jeremiah 23:5, 33:15, Zechariah 3:8, 6:12.) A similar development occurs with the term "Servant" in later chapters.

When the future cleansing comes, God will wash away all the filth and bloodstains of Jerusalem, with a spirit of "judgment" and "fire". The word translated "spirit" here is ruach, sometimes translated "breath."

Isaiah 4:5-6, Cloud of smoke, pillar of fire

Then the Lord will create over all of Mount Zion and over those who assemble there a cloud of smoke by day and a glow of flaming fire by night; over everything the glory will be a canopy. It will be a shelter and shade from the heat of the day, and a refuge and hiding place from the storm and rain.

When the future cleansing comes, God's presence will fill Zion as it did during the Exodus. God's glory will then be a "covering",  a "shelter" (tabernacle) over His chosen people.