Psalm 66 is a hymn of thanksgiving for God’s answer to a personal request.  Yet, it is written to highlight that God’s answers to one person are in context of his answering the prayers of the nation and of all the earth.

1-4 – Let all the earth worship the God of Israel based upon his awesome deeds.

5-7 – The singer describes the miracles of the Exodus as evidence of God’s awesome deeds, which result in the basis of all people worshipping God.

8-12 – The singer now recounts how God tested the Hebrew people and brought them through the Exodus to the promised land, a place of abundance.  God has a chosen a special people to bring light and knowledge of God to all the people of the world.

13-15 – Now, the singer gets personal and explains that his offerings at the sanctuary to thank God for answer to his personal prayer.  These offerings are not bribes but gratitude.

16-20 – Because God has answered his prayer, the singer is praising God for all to hear.  Each-and-every person should be able to thank and to praise God for their answered prayers.  Notice that one of the requirements for God to answer your prayer is that you must not cherish iniquity (sin) in your heart.  This is not a requirement to be sinless, but a reminder to thank God and to serve him better.