C. F. Keil and Franz Delitzsch on Jeremiah 15:18

Jer 15:18

Why is my pain become perpetual? "My pain" is the pain or grief he feels at the judgment he has to announce to the people; not his pain at the hostility he has on that account to endure. נצח adverbial = לנצח, as in Amo 1:11; Psa 13:2, etc. "My wound," the blow that has fallen on him. אנוּשׁה, malignant, is explained by "(that) will not heal," cf. Jer 30:12; Mic 1:9. The clause 'היו still depends on למּה, and the infin. gives emphasis: Wilt Thou really be? אכזב, lit., lying, deception, means here, and in Mic 1:16, a deceptive torrent that dries up in the season of drought, and so disappoints the hope of finding water, cf. Job 6:15. "A water," etc., is epexegesis: water that doth not endure. To this the Lord answers -