“The surviving remnant of the house of Judah will again take root downward and bear fruit upward.” – 2 Kings 19:30 (NASB)
This is principle that God applies. His purpose and His promises will never go undone. The context of today’s verse is a message God sent to the people living in Jerusalem. Isaiah was charged to deliver this message. Hezekiah was King and he was anxious about what would happen to his kingdom. The Assyrians had conquered the Northern 10 tribes and deported most of the people exchanging them for people from non-Jewish cultures under their control. God’s warning for many years through Isaiah, Jeremiah and other prophets was that the same lay in store for the Southern Kingdom. This conqueror was promised to be Babylon. Before this happens Hezekiah is promised a reprieve from the threat enjoined by Assyria. In this promise is God’s plan to preserve a remnant of the house of Judah (from whom the Messiah will come). This remnant will be what regenerates their people. From the remnant of survivors in Jerusalem would come the descendants who would cover the land once again. It would be many years but that promise is what happened and it is still happening today. God always preserves a remnant of the blessed to carry out fulfillments of His promises.