The first-born of the poor; the people of the Jews, who are brought to extreme poverty by the cruelty and the malice of other enemies. The first-born were the chief of all the children. Hence the title of first-born is given to persons or things which are most eminent in their kinds, as to the people of Israel, Exodus 4:22, to David, Psalms 89:27, to a grievous death, Job 18:13, and here to persons eminently poor. Shall feed; shall have plenty of provisions, in spite of all thine attempts against them. I will kill thy root; I will utterly destroy thee both root and branch, so that there shall not be a remnant of thy people reserved, as it follows. It is a metaphor from a tree, which for want of nourishment is dried up by the roots.
Related Commentaries of Isaiah 14:30
Isaiah 14:30
30 And the firstborn of the poor shall feed, and the needy shall lie down in safety: and I will kill thy root with famine, and he shall slay thy remnant.