Be not silent, O God of my praise!
That's how Psalm 109 opens. David reflects sentiments I suspect every believer has felt more than once, perhaps often. Certainly I have. There are issues you are certain are important to God - the salvation of a relative, the healing of a broken relationship, the feeding of an impoverished homeless person, a struggle with personal internal sin and unbelief, the redress of blatant injustice. Certainly, God would love to be engaged with these issues. No?
Haven't you prayed your heart out over such issues only to sense that God's attention is somewhere else? The enemy whispers, "See? He doesn't really care." or "I told you, He's incapable of doing what you ask."
The psalmist's issue
He is being slandered! "Wicked and deceitful mouths are opened against me." This from people who have experienced David's love. "In return for my love they accuse me...they reward me evil for good." I suspect that David penned this prayer when he was on the run from Saul or perhaps later when he had to flee Jerusalem to escape a rebellion mounted by his son, Absalom. In any case, he had good reason to be feeling betrayed. He wasn't paranoid.
Off the reservation!
For the next fifteen verses David spews out nothing but invective. "Appoint a wicked man against him...let his prayer be counted as sin!...May his days be few, may another take his office! May his children be fatherless and his wife a widow!...let there be none to extend kindness to him... He loved to curse, let curses come upon him...May this be the reward of my accusers from the Lord."
"That's not very nice of you, David! Your God is a God of love, no? If you were feeling these things, did you have to write them up and make them public? What will people think?" These are thoughts that even sympathetic Christians can't avoid. And non-Christians? Well, they relish ridiculing us over what they judge to be utterly inconsistent with good manners, let alone the love we tout.
A lot more on spiritually incorrect psalms
What to make of it
First off, note what David doesn't do. He does not take matters into his own hands to avenge the insults. Twice he spared Saul's life when he could have easily put an end to his tormentor. And rather than mount a military counter attack on Absalom, he went into exile. He continued to love his son and wanted to spare Jerusalem certain bloodshed. When, against his orders, Absalom was killed David mourns, "O my son, Absalom, my son, my son, Absalom! Would I have died instead of you, O Absalom, my son, my son!" (II Sam.18:33) Remember, that David was not a private citizen. As the rightful sovereign over his people he had every right to defend his throne against any who would usurp it. Yet he stayed his hand and gave himself to prayer. (Psalm 109:4)
When the Scriptures call us to love, we are not expected to be numb to pain or to be indifferent to justice. Integrity demands that we allow ourselves to experience the pain inflicted upon us. I said, "experience", not "controlled by". Big difference. And wisdom calls for us to seek justice, without taking the law into our own hands.
"Well, OK, but aren't David's sentiments a little over the top?" Be honest now. Haven't you entertained similar feelings? Judging by common angry expressions I hear ("Go to hell!", "I could kill him!", "F you!"), David's sentiments seem mild. The difference is that while we give ourselves to expletives and worse; David expresses himself to God, who alone can do anything about his grief.
What will God do?
Ultimately justice is guaranteed. Make no mistake, every sin receives its just reward either on the backs of the rebellious or on the cross of Jesus. Yes, we who know the Savior may boldly plead his forgiveness for the most hostile and negative sentiments we have. But God does more than lay the curse on Jesus. If we confess our sin, He is faithful and just not only to forgive our sin but to cleanse us from all unrighteousness. (I John 1:9) Notice how David experienced that cleansing. In the course of the prayer his heart is transformed from bitter resentment to joyful praise. "With my mouth I will give great thanks to the Lord; I will praise him in the midst of the throng." (vs.30) Yep! It's not just a private "Thank you, Lord"; but a public celebration of God's goodness.