Saul's instability grows. He gets more hostile to David until David has to flee for his life to Samuel. Saul's soldiers are stopped only by the Spirit making them prophesy. The same happens to Saul.
David is living with the real threat of enemies and death.
But God is his shepherd: He will feed and protect and sanctify him, and finally take him to live in His home forever.
David cries out for deliverance from enemies (Saul's soldiers) lying in wait to capture and kill him.
David doesn't deserve this. Bring them down and show the people they are in the wrong.
God has been and will be my fortress, so I will sing to Him.
How this is about Jesus
Israel's rulers sought unjustly to kill Him, too, but He trusted in God.
When we are assailed, we should first check if we deserve it. Can we say Psalm 59:3-4 honestly?
Put your trust in God, in the presence of enemies. Make Him your fortress.
It is okay to pray for the downfall of God's enemies, as long as personal vengeance isn't your motive.