As Israel decays, the Lord of the vineyard takes the dramatic step of cutting away the "main branches" or in other words the leading families, the recognized genealogical well-breds, or the families of rank and distinction. They were to be "burned" rather than further cultivated. (5: 7.) Their pride and arrogance disqualified them from preservation or further work. They were riddled with "decay" and unworthy of further effort. They were to be destroyed by fire. Fire is always a symbol of the Lord's judgments designed to cleanse or purge. Killing the decayed and corrupt leading families was cleansing the tree of the decay that had taken hold in the lofty, inner-circles of the people of Israel.
Men may have respected, even admired the success and status of these "main branches" of the Israelites, but that was nothing to the Lord. All their great rank, position, support structure and apparent security were nothing once the Lord decreed they were to be burned. Invading conquerors would target these specific social leaders for removal as a precaution against further loyalty. These would have to be removed for the outside ruler from a foreign power to succeed. The very thing which made them secure was the reason they were targeted to be killed. In a natural political purge the "main branches" who seemed forever entrenched to rule were swept away. No more would they "cumber the ground of [His] vineyard." (5: 9.)
To replace the notable families of distinction, the Lord determined to bring in "wild olive tree" branches, or those who have no distinction, or even family connections with the roots of Israel. (Id.) There would be new blood brought in by the conquerors with resultant intermarriages.
Unlike the main branches, there were "young and tender branches" which were not to be destroyed, but were instead to be transplanted. From Assyria or Babylon, these dislocated tribes would be spread into the nethermost part of the vineyard, or in the words of the Lord of the vineyard: "I will graft them whithersoever I will." (5: 8.)
With the mixing of foreign blood in the remaining "root" of the tree, and grafting of the "young and tender branches" into "wild" trees throughout the vineyard, the Israelite bloodlines become fragmented, scattered and no longer purely either Jacobian (by blood) or Israelite (by adoption). It would not matter if you look to the main root, or to the many scattered branches, they were all mingled with the "wild" gentile stock to produce a hybrid people. The corruption of the family was too deeply entrenched. They would not be able to repent any longer because their arrogance and ignorance prevented them from seeing their true condition. They thought themselves so highly favored of God they could not fall. Therefore, it was altogether necessary for them to fall. Without such a traumatic message delivered to the entire family, they would continue to presume safety meant they were justified. Any sign of prosperity was interpreted to mean they were right with God.
The family of Jacob needed this trauma for the covenant with Israel to be preserved. They were dying and not noticing it. Though it was terrible to endure, the Lord of the vineyard had the ultimate best interests of the entire tree in mind. He did what was needed to restore health and vigor. The covenant had been broken anyway, and this would make possible a renewal of the covenant and restoration from scattered Jacob the Family of Israel.