Just yesterday I read about this very issue of difficulty with certain Psalms in the book I’m reading, “Study Guide for the Rule of St. Benedict,” by Maria-Thomas Beil, O.S.B.:
“Others take issue with the language of war and revenge. We have to understand these themes historically, considering that Israel had always been a nation involved in battle and war. In their view, war was justified, if God helped them; if not, it was because of their infidelity that God abandoned them to their enemies. This demanded conversion on their part. In recent times, we have become more concerned about peace, human rights, the value of life and freedom, and wish that such an attitude were prevailing universally! But have we as a nation and society really so far progressed beyond hatred, bias, discrimination, oppression, exploitation, injustice, etc.? …Some people insist on praying the whole Psalter, but want to “Christianize” it: instead of praying against human enemies, they suggest praying for the elimination of evil in all its forms: falsehood, injustice, exploitation, violence, etc… Here we can also include evil elements like natural disasters, hunger, poverty, illness and war. We can use the war images as metaphors for spiritual and ascetic warfare. After all, there is still a battle to be fought against evil and the world in our own hearts. St. Paul was one of the first to employ warlike terms in a spiritual sense. We can ask ourselves, which are my enemies, my shadows and temptations I have to fight with? What weapons do I use?”
Hope this helps some.