v1: Belonging with chapter 3; the women desperate for even one man to take away their reproach. They are prepared to be in a polygamous relationship, rather than remain single and ashamed.
v2-6: A pointer to the restoration of Israel, centred on Mount Zion.
v2: The Branch of the Lord; Jesus Christ, unique, the only Branch. There will be the remnant in Israel, for many were already judged.
Isaiah uses the phrase "that day" to indicate the day of restoration of the people. The current rejection will be ended, as the glorious promises of God are fulfilled.
v3: Those remaining will be holy, set apart for God.
v4: The purging of the women of Zion and the people of Jerusalem, see 1.25, as a prelude to their restoration. God will use judgment and fire to purge His people.
v5: Cloud of smoke and fire (Ex 40.38) for guidance and for glory; this is a mark of the people set apart for God.
v6: The tabernacle, see 25.4; 32.2; the Lord our refuge. This is Jesus Christ, the man our refuge, God who became man.