If you are accustomed to the Liturgia Horarum, and you look in a 1961 Breviary, you will get a shock when you got to the Office Hymn for Vespers during Eastertide. Instead of Ad cenam agni providi you will find Ad regias agni dapes. This text is the piece of elegant Renaissance Latinity which Urban VIII substituted for the the fifth century text previously in use. The problem Pope Urban had with the original is that it was written when Latin was still a spoken language, a living and vivid vernacular, and its text is therefore, from the point of view of classical purists, full of irregularities. For example, it treats stolis (robes) as if it were istolis: which is how they pronounced st- in the 'Vulgar Latin' period*. Like most popular and subclassical texts, it has anacoloutha, diminutives, and 'intolerably' erratic systems of accented syllables. All this is why I like it. I even feel that the author was a considerable poet who actually used 'irregular' accentual patterns to emphasise words.
Urban's gang of resurrected Horaces so rewrote the second stanza that not a word of the original remained ... but perhaps by this point I have lost non-latinists. Never mind. If you have your English Hymnal to hand, you can find the original, translated by the incomparable John Mason 'Patrimony' Neale, at 125. You will find the Urbanist replacement at 128. You may feel that both, in their different ways, are good hymns. You are right. I just happen to feel that Vatican II was wise to mandate the restoration of original texts (although the 1968 revisers, foolishly, did straighten out the rhythms a bit). The Benedictines, incidentally, never did adopt the Urbanist texts. Moreover, the Renaissance version can miss things. Neale was convinced that the old text's description of Christ's blood as 'rosy' (roseo: 'light pink', because Roman roses were not modern cultivars) is explained by that fact that if a body is totally drained of blood, the last few drops are ... pink (how did he know? Was he right?).
*Grandgent writes thus about the prosthetic vowel: "The earliest Latin example is probably iscolasticus, written in Barcelona in the second century; it is found repeatedly, though not frequently, in the third century; in the fourth and fifth it is very common: espiritum, ischola, iscripta, isperabi ..." Isidore of Seville in the seventh century was the first to comment on it. It has, of course, left innumerable marks upon the lexicography of the Romance languages (e.g. stella>istella>etoile).