Their root shall be as rottenness; they shall be like a tree which not only withers in its branches, but dies and rots at the roots, and therefore is past all hopes of recovery. The sense is, They shall be destroyed both root and branch. Their blossom shall go up as dust; shall vanish (for so the word ascend or go up is oft used, as Exodus 16:14 Job 5:26 Jeremiah 48:15 Ezekiel 11:23,24) as the dust, which is blown away with every wind; or, shall be resolved into dust, and yield no fruit. They have cast away; which implies disobedience joined with contempt.
Related Commentaries of Isaiah 5:24
Isaiah 5:24
24 Therefore as the firef devoureth the stubble, and the flame consumeth the chaff, so their root shall be as rottenness, and their blossom shall go up as dust: because they have cast away the law of the LORD of hosts, and despised the word of the Holy One of Israel.