Albert Barnes Commentary Isaiah 14:30

"And the first-born of the poor shall feed, and the needy shall lie down in safety; and I will kill thy root with famine, and thy remnant shall be slain." — Isaiah 14:30 (ASV)

And the first-born of the poor shall feed - That is, there will be safety for those parts of Judah that have long been exposed to the invasions of the Philistines. Philistia bordered Judea and was constantly making war on it, so that no safety was felt. Isaiah now says that Hezekiah would so effectively and completely subdue them that there would be no danger from their invasion.

The phrase ‘the first-born of the poor’ is a Hebraism, a strong, emphatic expression, denoting the poorest, the most abjectly poor—those who have an exceptional level of need, just as the first-born among the Hebrews were entitled to special distinctions and privileges. The idea is that even the poorest and most defenseless would be safe.

Shall feed - That is, they will be supplied with food; they will feed safely as a flock does that is guarded from wild beasts. They will no longer be alarmed but will dwell in security, peace, and plenty.

And I will kill your root - The word translated ‘root’ properly denotes the root of a plant. When this root is dried up or killed, the plant, of course, withers and dies. So God says that He would effectively and entirely destroy the power of the Philistines.

Slay your remnant - That is, He will slay all that pertains to you. Or, He will dry up the root, and the branches will wither and die also. The whole power of the nation will be withered and destroyed.