HE FOLLOWING Apostolic Letter, Sacrificium Laudis, was sent by Pope Paul VI to religious groups obliged to the choral recitation of the divine office. It bears the date of 15 August 1966, the feast of the Assumption of the Blessed Virgin Mary.
Notice the strong words used by the Pope. For example:
“For while some are very faithful to the Latin language, others wish to use the vernacular within the choral office. [ … ] We have been somewhat disturbed and saddened by these requests.”
Your families, dedicated as they are to God, have always held in honour, as an offering from lips that confess to our Lord, the Sacrifice of Praise: that is, the psalms and hymns by which the hours, days and seasons of the year are hallowed with religious devotion, in the midst of which the Eucharistic Sacrifice shines, as it were like the sun, and draws all things to itself. With good reason is it held that nothing should be preferred to so holy a work as this. It is not difficult to perceive how much honor is rendered by it to the Creator of all things, or what benefits it confers upon the Church. You have proved, by following this fixed and unceasing manner of prayer, what importance divine worship has for human society.
Yet, from letters which some of you have sent, and from many other sources, We learn that discordant practices have been introduced into the sacred liturgy by your communities or provinces (We speak of those only that belong to the Latin Rite.) For while some are very faithful to the Latin language, others wish to use the vernacular within the choral office. Others, in various places, wish to exchange that chant which is called Gregorian for newly-minted melodies. Indeed, some even insist that Latin should be wholly suppressed.
We must acknowledge that We have been somewhat disturbed and saddened by these requests. One may well wonder what the origin is of this new way of thinking and this sudden dislike for the past; one may well wonder why these things have been fostered.
You yourselves know well how greatly We love your religious families, and how we value them. You can have no doubt of this. We have often marveled at the examples of outstanding holiness and the products of deep learning which ennoble them. We think it a happiness if We are able, in any lawful and fitting way, to support them, to comply with their wishes, to take thought for their betterment. 
Yet those things that We have mentioned are occurring even though the Second Ecumenical Vatican Council has after due deliberation declared its mind in solemn fashion (Sacrosanctum Concilium, 101, 1), and after the publication of clear norms in subsequent Instructions. In the first Instruction (ad exsecutionem Constitutionis de sacra Liturgia recte ordinandam), published on 26 September 1964, it was decreed as follows:
In celebrating the divine office in choir, clerics are bound to preserve the Latin language (n. 85).
In the second Instruction (de lingua in celebrandis Officio divino et Missa “conventuali” aut “communitatis” apud Religiosos adhibenda), published on 23 November 1965, that law was reinforced, and at the same time due consideration was shown for the spiritual advantage of the faithful and for the special conditions which prevail in missionary territories.  Therefore, for as long as no other lawful provision is made, these laws are in force and require the obedience in which religious must excel, as dear sons of holy Church.
What is in question here is not only the retention within the choral office of the Latin language, though it is of course right that this should be eagerly guarded and should certainly not be lightly esteemed. For this language is, within the Latin Church, an abundant well-spring of Christian civilization  and a very rich treasure-trove of devotion. But it is also the seemliness, the beauty and the native strength of these prayers and canticles which is at stake: the choral office itself, “the lovely voice of the Church in song” (Cf. St Augustine’s Confessions, Bk 9, 6). Your founders and teachers, the holy ones who are as it were so many lights within your religious families, have transmitted this to you. The traditions of the elders, your glory throughout long ages, must not be belittled. Indeed, your manner of celebrating the choral office has been one of the chief reasons why these families of yours have lasted so long, and happily increased. It is thus most surprising that under the influence of a sudden agitation, some now think that it should be given up.
In present conditions, what words or melodies could replace the forms of Catholic devotion which you have used until now? You should reflect and carefully consider whether things would not be worse, should this fine inheritance be discarded. It is to be feared that the choral office would turn into a mere bland recitation, suffering from poverty and begetting weariness, as you yourselves would perhaps be the first to experience. One can also wonder whether men would come in such numbers to your churches in quest of the sacred prayer, if its ancient and native tongue, joined to a chant full of grave beauty, resounded no more within your walls. We therefore ask all those to whom it pertains, to ponder what they wish to give up, and not to let that spring run dry from which, until the present, they have themselves drunk deep.
Of course, the Latin language presents some difficulties, and perhaps not inconsiderable ones, for the new recruits to your holy ranks. But such difficulties, as you know, should not be reckoned insuperable. This is especially true for you, who can more easily give yourselves to study, being more set apart from the business and bother of the world. Moreover, those prayers, with their antiquity, their excellence, their noble majesty, will continue to draw to you young men and women, called to the inheritance of our Lord. On the other hand, that choir from which is removed this language of wondrous spiritual power, transcending the boundaries of the nations, and from which is removed this melody proceeding from the inmost sanctuary of the soul, where faith dwells and charity burns – We speak of Gregorian chant – such a choir will be like to a snuffed candle, which gives light no more, no more attracts the eyes and minds of men.
In any case, beloved Sons, the requests mentioned above concern such grave matters that We are unable to grant them, or to derogate now from the norms of the Council and of the Instructions noted above. Therefore we earnestly beseech you that you would consider this complex question under all its aspects. From the good will which we have toward you, and from the good opinion which we have of you, We are unwilling to allow that which could make your situation worse, and which could well bring you no slight loss, and which would certainly bring a sickness and sadness upon the whole Church of God. Allow Us to protect your interests, even against your own will. It is the same Church which has introduced the vernacular into the sacred liturgy for pastoral reasons, that is, for the sake of people who do not know Latin, which gives you the mandate of preserving the age-old solemnity, beauty and dignity of the choral office, in regard both to language, and to the chant.
Obey, then, these prescriptions sincerely and calmly. It is not an excessive love of old ways that prompts them.  They derive, rather, from Our fatherly love for you, and from Our concern for divine worship.
Finally, We impart most willingly to you and to your religious, as an earnest of heavenly gifts and as a sign of Our favour, the apostolic Blessing in our Lord.
 Reading consulendi (“consulting the interests of”) for consuendi (“stitching together”).
 The second “Instruction” allowed for the use of vernacular when religious communities in charge of “a parish, a shrine, or a church attended by large numbers of the faithful” recited some part of the office with the faithful. One can regret the looseness of this prescription; but the present text, coming as it does from the supreme legislator, must rank as an authentic interpretation of it. In other words, the religious communities whom the pope is addressing may not consider Latin to be the exception and the vernacular normal.
 The translators of the authoritative collection entitled “Documents on the Liturgy, 1963-1979: Conciliar, Papal and Curial Texts” (DTL) render christiani cultus humani simply as “culture,” rather than as “Christian civilization”.
 Quas non immodicus amor morum veterum suggerit. DTL renders this phrase, “the commands that a great love for your own ancient observances itself suggests”; but it appears rather that Pope Paul is here anticipating a likely objection to his commands. Immodicus means not “small” but “excessive” or “exaggerated”.