It is not unreasonable to suppose that the life of prayer will draw us into a genial camaraderie, so secure in God’s grace and confident in his beneficence that we are irresistibly carried along in the flow of the river of God, viewing everyone and everything with the cheeriest of feelings. But reason, at least reason inexperienced and untested in the life of prayer, isn’t the best guide in these matters. When we take the Psalms as our guide, we find that people who pray have a lot of enemies, and that they spend a lot of their praying time dealing with them.
Most of us would prefer it otherwise. We commonly indulge our preference by subjecting the Psalms to severe editing, cutting away any negativism that offends piety and disturbs the peace. The editing is usually unconscious, accomplished by the simple expedient of withdrawing the imagination and sliding over the offensive passages. Psalm 137 is on nearly everyone’s list for revision. Psalm 137 is the scandal of the Psalter.
– Eugene Peterson, Answering God: The Psalms as Tools for Prayer