Saul comes to the cave to attack David, but David ends up cutting a part of Saul's robe. David's supporters think he should have killed Saul, yet David thinks he has done too much to Saul. David seems to respect Saul just because he is king.
A few chapters (in Saul) later, David again has the opportunity to kill Saul. Saul is asleep. David and his supporters and he find Saul sleeping. Rather than kill Saul, David steals his spear and his water jug.
Do I have that kind of mercy? If I had the opportunity to harm one of my enemies would I? Lucado writes that "Vengeance fixes your attention at life's ugliest moments."
David continues his "God focus" and repeatedly describes Saul as "the Lord's anointed." That is why he spares Saul - because God has chosen Saul for some reason.
Lucado writes that God is not finished with our enemies. The fact that they have a pulse is proof that God still wants them around, as one of His projects. "Revenge removes God from the equation. Vigilantes displace and replace God. Only God assesses accurate judgments." We lack the knowledge and understanding to be completely fair. Our emotions cloud our judgement. We are human.
David does, however, avoid Saul. We can avoid our enemies too.
Forgiveness, according to Lucado, is to move on. "You don't excuse him, endorse her, or embrace them. You just route thoughts about them through heaven. You see your enemy as God's child and revenge as God's job."