John Paul II states in his Wednesday Audience of November 2001, reflecting on Psalm 117 that “It is a short doxology, namely, an essential hymn of praise, that ideally functions as the conclusion of longer psalms.”
1 O praise the Lord, all ye nations: praise him, all ye people.
In Romans 15, Paul uses the first verse of the Psalm to invite the peoples of the world to glorify God. Just before this, it is said “But that the Gentiles are to glorify God for his mercy, as it is written: Therefore will I confess to thee, O Lord, among the Gentiles, and will sing to thy name.”
Many of the Psalms have the people of Israel going so far as to call down a curse on the enemies of Israel. They glorify, certainly, the Lord, but also glorify Israel as the people set apart. Here, the Psalm is used by the great Old Testament scholar (if we may call him so) St. Paul as a call to all nations.
In Athens, Paul exhorts them “standing in the midst of the Areopagus, said: ‘Ye men of Athens, I perceive that in all things you are too superstitious. For passing by, and seeing your idols, I found an altar also, on which was written: To the unknown God. What therefore you worship, without knowing it, that I preach to you.’”
It is time for all nations to praise the Lord, the one true God. There had always been those who seek God but have not heard (how can they believe if they have not heard?) the revelation of His salvation. One such example “was a certain man in Caesarea, named Cornelius, a centurion of that which is called the Italian band; A religious man, and fearing God with all his house, giving much alms to the people, and always praying to God.”
There are many like Cornelius today. Many who have not heard the truth but seek it. Of course, in their very seeking, the grace of God is at work in them. Undeservedly, God moves them ever closer, opens their hearts to the good news, and this is all to the praise of His great mercy:
2 For his mercy is confirmed upon us: and the truth of the Lord remaineth for ever.