John Gill Commentary Jeremiah 9:15

"therefore thus saith Jehovah of hosts, the God of Israel, Behold, I will feed them, even this people, with wormwood, and give them water of gall to drink." — Jeremiah 9:15 (ASV)

Therefore thus says the Lord God of hosts, the God of Israel ,
&c.] He calls himself "the Lord God of hosts", of armies above and below, in heaven and in earth, in opposition to Baalim, the idols of the Gentiles; which word signifies "lords"; which, though there be many who are called so, there is but one God, and one Lord, who is God over all, and "the God of Israel"; who had chosen them, and distinguished them by the blessings of his goodness; and yet they had forsaken him, and followed after other gods; by which the eyes of his glory were provoked, and he was determined to chastise them for it:

behold, I will feed them, even this people, with wormwood ;
that is, with straits or difficulties, as the Septuagint version; with bitter afflictions; such are not joyous, but grievous; which are irksome and disagreeable, as bitter things, and particularly wormwood, are to the taste. The Targum is,

``I will bring tribulation upon them, bitter as wormwood:''

and give them water of gall to drink ;
meaning either of the entrails of a beast so called, or of the juice of the herb hemlock, as the word is rendered in (Hosea 10:4) , as Kimchi; or of the poison of a serpent, as Jarchi; and so the Targum, ``and I will give them the cup of cursing to drink as the heads of serpents:'' signifying that their punishment would be very severe, though just.