Because — They rejoiced at the ruin of the Jews. Fat — The cause for which Babylon is threatened, was doubtless their luxury of all sorts commonly attending great wealth.
Related Commentaries of Jeremiah 50:11
Jeremiah 50:11
11 Because ye were glad, because ye rejoiced, O ye destroyers of mine heritage, because ye are grown fatd as the heifer at grass, and bellow as bulls;