Psalm 17 is a prayer for vindication against human persecutors. The psalmist may have been praying in the night (vv. 3, 15) Verse 8 includes two idioms which, if you think about them, are odd.
Guard me as the apple of the eye;
hide me in the shadow of your wings....
Do eyes have apples? Does God have wings?
The "apple of the eye" expression translates a Hebrew phrase that is more literally "the little person of your eye." Maybe this is a reference to the tiny reflection of one's self that can be seen in another person's eye. Whatever it is, it seems to ask God to keep a close watch over the one praying.
Whether God's wings are supposed to be literal or metaphorical I just don't know.
At 50 verses, Psalm 18 is the longest we've encountered so far. It is a psalm of thanksgiving for victory in battle. The ascription in the heading suggests just such a circumstance in the life of David.
The psalmist believes that God fought on his side. God is described in fearsome terms (v. 8):
Smoke went up from his nostrils,
and devouring fire from his mouth;
glowing coals flamed forth from him.
I remember once seeing the first verse of Psalm 19 painted on a satellite dish antenna beside a church.
The heavens are telling the glory of God
I wondered at the time what the church used that antenna for. The first part of this psalm (vv. 1-6) praises God for creation. The second part (vv. 7-13) praises God for the Torah. I've heard preachers use the last verse (v.14) as a prelude to their sermon:
Let the words of my mouth and the meditation of my heart
be acceptable to you,
O Lord, my rock and my redeemer.
Psalm 20 is a prayer of blessing pronounced over a king riding out to war.
And just because he sings about the apple of his eye, here's a little Stevie Wonder...
Give victory to the king, O Lord;
answer us when we call.
Next: Psalms 21-25