9:8 judge the world in righteousness. Paul apparently refers to this promise in Acts 17:31, referring to the resurrected Christ as the coming Judge.

9:10 hast not forsaken. God has promised never to forsake those who “put their trust” in Him (Hebrews 13:5). Yet He did forsake the only one who was perfectly righteous and had perfect trust in the heavenly Father (Matthew 27:46)! But that was only until the world’s sin-debt had been fully paid by His willingness to be made sin and suffer the awful absence—for a time—of His Father. Then, “when He cried unto Him, He heard” (Psalm 22:24).

9:12 inquisition. That is, “inquiry.”

9:13 liftest me up. When this psalm is seen as a Messianic psalm, this verse becomes a glorious promise of the resurrection of the Son whose death had been engineered by His enemies.

9:16 Higgaion. Higgaion is another Hebrew term of uncertain meaning. Combined with “Selah,” the intent is probably to call for exultant meditation of the marvelous truths just revealed.

9:17 turned into hell. Not only will the wicked be sent into hell (that is, sheol, there to await the final judgment), but so also all those who may seem relatively upright morally but have ignored God’s provision for their salvation. The word “nations” is from the Hebrew word for “heathen” or “Gentiles” (same as rendered “heathen” in Psalm 9:5,19, and “nations” again in Psalm 9:20.

9:19 Arise, O LORD. This is the second of ten invocations in the Psalms to the Lord to “arise” (the first is at Psalm 3:7 and the last at Psalm 132:8). It answers to the final plea in the New Testament: “Even so, come, Lord Jesus” (Revelation 22:20)