You've probably heard the expression, "Make a joyful noise unto the Lord." Psalm 66 is one of those occasions where we hear this imperative. For those of us who have difficulty singing, being told to simply make a joyful "noise" sounds very reassuring and feasible!
The rest of this psalm answers the question of why a joyful noise should be made to God.
Verses 5-7 are a reminder of the Passover events and the deliverance through the parting of the Red Sea. The same God who rescued the Israelites back then is still the same one today, and still worthy of praise for His acts of salvation!
Verses 8-12 is a call to praise...for suffering! The psalmist reflects on the trials of his nation: they have endured despite being tested and refined like silver, being ensnared and burdened, and being ruled over by others. Even though they have been "through fire and through water," the psalmist rejoices that God is still with them.
Verses 13-15 is a promise by the psalmist to fulfill his vows through the sacrificial offerings of rams, bulls and goats. God had delivered him from trouble, and now it is his turn to thank God and praise God.
Verses 16-20 is a personal testimony of God's faithfulness. God is to be praised because He answers prayer and remembers His servants. As the psalmist concludes, "Blessed be God, because he has not rejected my prayer or removed his steadfast love for me" (vs. 20).