Jeremiah 8:18 - Ellicott's Commentary On The Whole Bible

When I would comfort myself... — The word translated comfort is not found elsewhere, and has been very differently understood. Taking the words as spoken after a pause, they come as a cry of sorrow following the proclamation of the judgment of Jehovah, Ah, my comfort against sorrow! (mourning for it as dead and gone); my heart is sick within me. The latter phrase is the same as in Isaiah 1:5.