Albert Barnes Commentary Isaiah 39:7

"And of thy sons that shall issue from thee, whom thou shalt beget, shall they take away; and they shall be eunuchs in the palace of the king of Babylon." — Isaiah 39:7 (ASV)

And of that sons - Your posterity (see the note at Matthew 1:1).

That shall issue from you - Of the royal family. The captivity at Babylon occurred more than a hundred years after this, and of course those who were carried there were somewhat remote descendants of Hezekiah.

And they shall be eunuchs - The word used here (סריסים sâriysiym) denotes properly and strictly eunuchs, or such persons as were accustomed to attend on the harems of Oriental monarchs (Esther 2:3, Esther 2:14–15). These persons were also employed often in various offices of the court (Esther 1:10, Esther 1:12, Esther 1:15), and hence, the word often means a minister of court, a court-officer, though not literally an eunuch (Genesis 37:6; Genesis 39:1).

It is not easy, however, to tell when the word is to be understood literally, and when not. The Targum understands it of those who should be nurtured, or become great in the kingdom of Babylon. That the Jews were advanced to some offices of trust and power in Babylon, is evident from the case of Daniel (Daniel 1:2–7).

It is by no means improbable, also, that the king of Babylon would have a pride in having among the attendants at his court, or even over the harem, the descendants of the once magnificent monarchs of the Jews.