A C.S. Lewis quote that comes frequently to mind these days:
The practical problem about charity (in our prayers) is very hard work, isn’t it? When you pray for Hitler & Stalin, how do you actually teach yourself to make the prayer real? The two things that help me are (a) A continual grasp of the idea that one is only joining one’s feeble little voice to the perpetual intercession of Christ, who died for those very men (b) A recollection, as firm as one can make it, of all one’s own cruelty wh. might have blossomed, under different conditions, into something terrible. You and I are not, at bottom, so different from these ghastly creatures.