The God of my mercy shall prevent me: God shall let me see my desire upon mine enemies. - Psalm 59:10
Unto thee, O my strength, will I sing: for God is my defence, and the God of my mercy. - Psalm 59:17
Not once, but twice in the span of a few verses, David declared God as the God of his mercy. Notice the wording there. It's easy to read right through that and see "God of mercy," which God certainly is, but that's not what it says. It says "the God of my mercy." To understand the meaning, we need to comprehend the storyline in which this psalm takes place.
At this point, King Saul has just tried to kill David because of his jealousy over the people's loyalty to David. Even though Saul didn't know about David's secret anointing as the next king, he felt threatened by David's abilities and growing popularity. So, he sought to kill him, and David had to sneak out of his own house to save his life. It is in the midst of this turmoil and chaos that David wrote Psalm 59.
If anyone had cause to get even, it was David. If anyone felt the need to strike back against those who had wronged him, it was the psalmist. But instead, we find him thanking God for not only giving him mercy but also for instilling mercy in him to show unto others. We know from later events that David was not above premeditated murder. The people were for him long before he was king. He had already been promised the kingdom. All he had to do was get rid of Saul—the man who had just tried to kill him. He could have staged a palace coup. He could have taken matters into his own hands and sought retaliation beyond self-preservation. But instead, he showed mercy. And in the myriad of emotions that consumed David during this time, the psalmist felt led to note that the desire to show mercy had to come from God because it certainly didn't stem from the flesh.
Matthew Henry put it this way: "It is very comfortable to us, in prayer, to eye God, not only as the God of mercy but as the God of our mercy, the author of all good in us and the giver of all good to us." We are nothing in and of ourselves, and nothing good resides within us save the Holy Spirit (for those who are saved, of course). Any good that we do comes directly from Him. He is the source of the compassion we show to the needy, the love we portray to the unlovable and the mercy we pour out upon the undeserving. That is, after all, what mercy is. It is the act of giving goodness and forgiveness to those who don't deserve it. Just as God pours out His mercy upon us day after day, so does He expect us to do the same for others. As we are forgiven, so should we forgive.
One last thing I want to point out is this: in verse 10 of chapter 59, the psalmist says,
The God of my mercy shall prevent me.
The word "prevent" here means "to go before," which leads us to conclude that the God of our mercy will go before us. That alone is worthy of praise, but if we'll look at the familiar passage of Psalm 23, verse 6 tells us,
Surely goodness and mercy shall follow me all the days of my life: and I will dwell in the house of the Lord for ever.
Now mercy is following us. Mercy ahead. Mercy behind. God's mercy and the God of mercy Himself have us surrounded. There is no escape, not that we would want to. But it's also imperative to remember that mercy is within us if we have the Spirit of God; therefore, we should be givers of that great mercy and not receivers only.
While David was far from perfect, in this, he did well. Until his dying day, he loved and respected Saul. Despite Saul's many attempts on David's life, the psalmist allowed mercy to flow. Will we do the same?