1.

LORD, how are they increased that trouble me! many are they that rise up against me.

Title. A Psalm. See App-65 .
when. The first psalm with an historical title. See App-63 and App-64 . Compare 2 Samuel, chapters 15-18.
how . . . ! Figure of speech Exclamatio ( App-6 ), for emphasis.
increased = multiplied.
Many = what multitudes.

2.

Many there be which say of my soul, There is no help for him in God. Selah.

Many. Figure of speech Anaphora.
my soul = me, or myself. Hebrew. nephesh . App-13 .
help = salvation, or deliverance.
God. Hebrew. Elohim. App-4 .
Selah. Connecting the contrast between "man" (as a creature) who knows God (Elohim) only as Creator, with the speaker (David), who knew Jehovah as his Covenant God. See App-4 and Psalms 66:11 .

3.

But thou, O LORD, art a shield for me; my glory, and the lifter up of mine head.

art a shield. Figure of speech Metaphor ( App-6 ); "shield" put by Figure of speech Metonymy (of Adjunct), App-6 , for defence.
for m e = about me.
mine head. Figure of speech Synecdoche (of Part), App-6 , put for whole person.

4.

I cried unto the LORD with my voice, and he heard me out of his holy hill. Selah.

cried = shall cry.
heard = will answer.
holy hill. See note on Psalms 2:6 .
Selah. Connecting the peace which comes from prayer, as in Philippians 1:4 , Philippians 1:6 . See App-66 .

5.

I laid me down and slept; I awaked; for the LORD sustained me.

slept = have slept. At Mahanaim (2 Samuel 17:27-29 ).
sustained = was sustaining.

6.

I will not be afraid of ten thousands of people, that have set themselves against me round about.

7.

Arise, O LORD; save me, O my God: for thou hast smitten all mine enemies upon the cheek bone; thou hast broken the teeth of the ungodly.

ungodly = lawless. Hebrew. rasha'. App-44 .

8.

Salvation belongeth unto the LORD: thy blessing is upon thy people. Selah.

Salvation = deliverance, same word as "help", Psalms 3:2 .
Thy blessing is = Thy blessing hast been, and wilt be: i.e. whatever may happen to me. In this spirit he sends back the Ark (2 Samuel 15:25 .
Selah. Connecting Psalms 3 with Psalms 4 , which has the same subject. See App-66 .
To the chief Musician. See App-64 .
Neginoth = smitings; from nagan, to strike, as on strings. See App-65 . Here the reference is to the smitings with words in Psalms 3 , as in Lamentations 3:63 (compare Job 30:9 . Lamentations 3:14 ). Compare the other Neginoth Psalms: Psalms 3:2 ; Psalms 5:6 ; Psalms 53:1 ; Psalms 54:3 ; Psalms 60:1 , Psalms 60:11 , Psalms 60:12 ; Psalms 66:10-12 ; Psalms 75:4-6 (Compare Psalms 77:7 , Isaiah 38:20 , and Habakkuk 3:19 ).