This is Psalm 99 (100) by Joseph Gelineau.
The verses are free chant so I only will do backings for the two antiphons.
Arise, come to your God, sing him your songs of rejoicing.
Alelluia x3
The full text is in the samples at Hymnary.
I suppose if they were to be used these days you would need the revised Grail texts which can purchased at GIA.
STOP PRESS
Thank God for Chris Wroblewski who runs the LiturgyShare site, where I have been spending a lot of time lately. He has sent some commentary on this one and Gelineau psalms in general. He notes that this is a necessarily brief and incomplete exposition:
I don’t believe “free chant” is a good description for a Gelineau psalm, as they have a fixed (so-called “sprung”) rhythm. You could make a backing with the verses because each measure has a fixed length as shown in the score: it’s the cantor’s job to fit the words into each pulse, which makes them very difficult for those of us who don’t have good timing skills, but much easier for the accompanist as they can just play normally. The notes in parentheses at the start of each phrase are always played, but the downbeat notes are for the singers, who have to work out where to start so that the finish of that measure allows them to smoothly transition into the next measure. In some later Gelineau psalms you will see brackets in some cantors lines: they indicate measures not to be played in that particular verse.
I have a copy of the GIA book you reference at the end of your post. The revised text does not give any consideration to Gelineau, whereas the original translation was written with Gelineau at the forefront. This results in it not fitting the Gelineau tones as well and seriously damages his most famous setting – Psalm 23 (22) (The Lord is my Shepherd / My Shepherd Is the Lord, #248 in NLPHB). There is no reasons the original Grail versions can’t be used as, say, a Communion hymn with those in the procession still able to sing the refrain, but the current Australian rubrics do allow previously approved psalm texts to still be used for the responsorial psalm.
He also sent some music files for learning purposes:
Antiphon
Arise, come to your God, sing him your songs of rejoicing.
1 Cry out with joy to the Lord, all the earth.
Serve the Lord with gladness.
Come before him, singing for joy.2 Know that he the Lord, is God.
He made us, we belong to him,
We are his people, the sheep of his flock.3 Go within his gates giving thanks.
Enter his courts with songs of praise.
Give thanks to him and bless his name.4 Indeed, how good is the Lord,
Eternal his merciful love;
He is faithful from age to age.5 Give glory to the Father Almighty,
To the Son, Jesus Christ, the Lord,
To the Spirit who dwells in hearts.
On a different note looking at our collective futures, this isn’t a Gelineau psalm, it is a Suno Psalm 100. It is AI and technically soulless soul music:


