Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Psa 66:1-7) Praise for God's sovereign power in the creation.
(Psa 66:8-12) For his favour to his church.
(Psa 66:13-20) And the psalmist's praise for his experience of God's goodness.
The holy church throughout all the world lifts up her voice, to laud that Name which is above every name, to make the praise of Jesus glorious, both by word and deed; that others may be led to glorify him also. But nothing can bring men to do this aright, unless his effectual grace create their hearts anew unto holiness; and in the redemption by the death of Christ, and the glorious deliverances it effects, are more wondrous works than Israel's deliverance from Egyptian bondage.
The Lord not only preserves our temporal life, but maintains the spiritual life which he has given to believers. By afflictions we are proved, as silver in the fire. The troubles of the church will certainly end well. Through various conflicts and troubles, the slave of Satan escapes from his yoke, and obtains joy and peace in believing: through much tribulation the believer must enter into the kingdom of God.
We should declare unto those that fear God, what he has done for our souls, and how he has heard and answered our prayers, inviting them to join us in prayer and praise; this will turn to our mutual comfort, and to the glory of God. We cannot share these spiritual privileges, if we retain the love of sin in our hearts, though we refrain from the gross practice, Sin, regarded in the heart, will spoil the comfort and success of prayer; for the sacrifice of the wicked is an abomination of the Lord. But if the feeling of sin in the heart causes desires to be rid of it; if it be the presence of one urging a demand we know we must not, cannot comply with, this is an argument of sincerity. And when we pray in simplicity and godly sincerity, our prayers will be answered. This will excite gratitude to Him who hath not turned away our prayer nor his mercy from us. It was not prayer that fetched the deliverance, but his mercy that sent it. That is the foundation of our hopes, the fountain of our comforts; and ought to be the matter of our praises.