God's Sovereign Mercy

Why did David want to show mercy to anyone in Saul's house? Why would God Himself show mercy to anyone? How is it that God shows Mercy? How does God's mercy make sinners His own? How is David a picture of the LORD Jesus Christ in His sovereignty as God? What is God's providence? How is God the first cause of all things? How do we see that mercy does not originate in anyone but God? Why would a Holy God show mercy to any of His lame and useless enemies? How is Jonathan a type of Christ?