On this third Sunday, and on the two that follow before the Ascension, the Church exhorts us to rejoicing and exultation for the Resurrection and Ascension of Christ, wherefore the Introit of this Sunday begins, ‘Shout with joy to God, all the earth.’ And there follows Alleluia, because this shout of joy is the exultation which the mind has for eternal things, and is to be made only to God. There follows, ‘Sing a psalm to His name’, that is, praise him with cheerful work, and likewise there follows a single Alleluia, because all other things arise from a single root, which is charity. There follows, ‘Give glory to His praise’, and there follows at the end a triple Alleluia, because from the power of the Father, and the wisdom of the Son, and the goodness of the Holy Spirit does it come about that He delivered us through His Passion and Resurrection, and therefore is God to be praised. But although there is exultation, nevertheless fear is also inculcated, lest hope without fear grow wanton unto presumption. (William Durandus, Rationale Divinorum Officiorum, 6, 94, 1)
Introitus (Ps 65) Jubiláte Deo, omnis terra, allelúia: psalmum dícite nómini ejus, allelúja: date glóriam laudi ejus, allelúja, allelúja, allelúja. V. Dícite Deo, quam terribilia sunt ópera tua, Dómine! in multitúdine virtútis tuæ mentientur tibi inimíci tui. Glória Patri. Sicut erat. Jubiláte Deo.Introit Shout with joy to God, all the earth, alleluia, sing ye a psalm to His name, alleluia; give glory to His praise; alleluia, alleluia, alleluia. V. Say ye unto God, How terrible are thy works, o Lord! in the multitude of thy strength thy enemies shall lie to thee. Glory be to the Father... As it was in the beginning... Shout with joy to God...
This Psalm has in the title the inscription, ‘For the end, a song of a Psalm of Resurrection’. When you hear ‘for the end’ (in the titles of various Psalms), understand it to mean ‘for Christ’, as the Apostle says, ‘For the end of the law is Christ, for righteousness to every one that believeth.’ (Rom. 10,4) ... ‘Jubilate unto God every land.’ What is jubilate? Break forth unto the voice of rejoicings, if you cannot break forth into words. For jubilation is not of words, but the sound alone of men rejoicing is uttered, as of a heart laboring and bringing forth into voice the pleasure of a thing imagined which cannot be expressed. ... ‘Say ye to God, How to be feared are Your works!’ Wherefore to be feared and not to be loved? Hear another voice of a Psalm (2, 11): ‘Serve the Lord in fear, and exult unto Him with trembling.’ What does this mean? Hear the voice of the Apostle: ‘With fear, he says, and trembling, work out your own salvation.’ Wherefore with fear and trembling? He has also given the reason: for God it is that works in you both to will and to work according to good will. (Phil. 2, 12-13) If therefore God works in you, by the Grace of God you work well, not by your strength. (St Augustine, Treatise on Psalm 65. The term ‘a psalm of Resurrection’ is in the title of the Greek and Latin translations of the Psalter.)