The second double "therefores"(cf. vv. 13, 14) announce God's judgment for the sins mentioned in verses 18-22, but also those identified since verse 8. The condemnation is cumulative.
5:24 The people had challenged God to act speedily (v. 19), and Isaiah assured them that He would. God in judgment is seen as a external fire that would consume His people. He would also be to them as an internal disease that decimates a whole plant, from roots to shoots. The reason for judgment is the people's rejection of mighty Yahweh's revealed will (cf. v. 12).
5:25 In fact, many judgments had already come against Judah in her history. God was removing the hedge and breaking down the wall around His vineyard (cf. v. 5). Nevertheless the nation had not repented, so more judgment would come.
