Psalms 136:10 - Ellicott's Commentary On The Whole Bible

For his mercy. — Here the refrain, after the mention of the destruction of the Egyptian first-born, and subsequently after that of war and slaughter, sounds harsh to Christian ears. But the word mercy (khesed) in the Hebrew motto implies distinctly covenant grace, that special favour of Jehovah in which the heathen did not share, and which was often most signally shown in their destruction.