English Basic Explanation - Chapter 66
This Psalm opens with the jubilant exclamation, "Shout [in praise] to God, all the earth!" which sets the festive, euphoric tone of this chapter. The impression one has when reading this Psalm is that David can hardly contain his joy, and in unbridled ecstasy he summons all inhabitants on earth to join him in praising God and extolling His greatness.
The cause for David's joy is indicated in verses 10-12, where he speaks of the trials and tribulations that Am Yisrael have endured and from which they have been extricated. They have been "purged" like metal (verse 10), imprisoned (verse 11) and brought through fire and water (verse 12), and are now able to jubilantly celebrate their salvation. God has heard their prayers and overlooked their misdeeds, and has brought them from crisis to deliverance (verses 17-20).
David announces his plans to fulfill the pledges he made during the period of hardship to bring expensive animal offerings to the Bet Ha'mikdash (verses 13-15), and then summons "all who fear God" to hear him describe what the Almighty has done for him (verse 16). This brings to mind the Korban Toda, the thanksgiving offering that was brought by a person who had been rescued from danger. It was customary to invite family and friends to partake of the sacrificial meat and to hear of the person's experiences, so that God's greatness and kindness would be publicized. Thus, as David announces his plans to offer thanksgiving offerings, he extends an invitation to all God-fearing men to join him in his celebration and hear of the wonders of the Almighty.
Several commentators explain this Psalm as a song of praise composed for the time of the final redemption. It thus offers us a glimpse of the exuberance and euphoria that the Jewish people will experience upon being delivered from the enemy nations and having the opportunity to once again serve the Almighty in the rebuilt Bet Ha'mikdash.