1. Psalm 9 is a psalm of thanksgiving. Much of the praise is for God's deliverance. Someone important is talking, maybe a king. The title styles it a "psalm of David," and we can read the psalm that way, although David really didn't face "the nations" (9:5). The psalmist speaks of God blotting out the names of his enemies (9:3).
The LORD is praised for the way he looks out for the oppressed (9:9). He avenges blood (9:12). God saves the psalmist from the gates of death, which are contrasted with the gates of Zion (9:13-14). Those who forget the poor and needy will be judged (9:18). In language that reminds us of Psalm 82, the nations will be judged; they will be reminded that they are human (9:19-20).
If the author is not David or Solomon, the mention of Zion suggests that this is a psalm of the southern kingdom.
2. There is some reason to believe that Psalm 9 and 10 were at some point one psalm, and the Greek translation of the psalms has them together as one psalm.
3. There is interesting language of God in the psalm. Most of the psalm refers to the LORD, YHWH. But there is also the expression el elyon, "God Most High" (9:2). This is a reference to YHWH as the king of the gods, as it were, the highest God. Twice he is said to be on his throne (9:4, 7). He is the judge of the world (9:7).
4. Death is referred to as "Sheol," the realm of all the mindless dead. We have already mentioned the image of the "gates of death" (cf. Matt. 16:18).
5. This is the first psalm where we encounter the term "selah." We just aren't sure what it meant. It could have meant a pause. It could have been a musical cue. We just don't know. The same goes for the term higgaion
A new set of instruction begins. The child is encouraged to listen to the preacher's teaching with the hope of a long life in result. The child should "wear" the teaching around his or her neck. It will lead to a good reputation.
Psalm 1 and Proverbs 1:1-7
Psalm 2 and Proverbs 1:8-14
Psalm 3 and Proverbs 1:15-19
Psalm 4 and Proverbs 1:20-27
Psalm 5 and Proverbs 1:28-33
Psalm 6 and Proverbs 2:1-5
Psalm 7 and Proverbs 2:6-15
Psalm 8 and Proverbs 2:16-22