Names/memories/memorials: David recounts (i.e. tells memories of) the Lord and sings praises to His name. The Lord blots out the name of the wicked as well as any memories of them. Therefore everyone should put their trust in His name and tell of His deeds.
Up/down language similar to Psalm 3 The wicked start on top, but are sinking down into the pit, and ultimately down into Sheol. But those who start on the bottom (David at the gates of death, the poor, the needy) will be lifted up. The Beatitudes were nothing new – they retell the original pattern of the original Kingdom.