How the Mattin office was not appointed by an ancient tradition but was started in our own day for a definite reason.
But you must know that this Mattins, which is now very generally observed in Western countries, was appointed as a canonical office in our own day, and also in our own monastery, where our Lord Jesus Christ was born of a Virgin and deigned to submit to growth in infancy as man, and where by His Grace He supported our own infancy, still tender in religion, and, as it were, fed with milk. 734 For up till that time we find that when this office of Mattins (which is generally celebrated after a short interval after the Psalms and prayers of Nocturns in the monasteries of Gaul) was finished, together with the daily vigils, the remaining hours were assigned by our Elders to bodily refreshment. But when some rather carelessly abused this indulgence and prolonged their time for sleep too long, as they were not obliged by the requirements of any service to leave their cells or rise from their beds till the third hour; and when, as well as losing their labour, they were drowsy from excess of sleep in the daytime, when they ought to have been applying themselves to some duties, (especially on those days when an unusually oppressive weariness was caused by their keeping watch from the evening till the approach of morning), a complaint was brought to the Elders by some of the brethren who were ardent in spirit and in no slight measure disturbed by this carelessness, and it was determined by them after long discussion and anxious consideration that up till sunrise, when they could without harm be ready to read or to undertake manual labour, time for rest should be given to their wearied bodies, and after this they should all be summoned to the observance of this service and should rise from their beds, and by reciting three Psalms and prayers (after the order anciently fixed for the observance of Tierce and Sext, to signify the confession of the Trinity) 735 should at the same time by an uniform arrangement put an end to their sleep and make a beginning to their work. And this form, although it may seem to have arisen out of an accident and to have been appointed within recent memory for the reason given above, yet it clearly makes up according to the letter that number which the blessed David indicates (although it can be taken spiritually): “Seven times a day do I praise Thee because of Thy righteous judgments.” 736 For by the addition of this service we certainly hold these spiritual assemblies seven times a day, and are shown to sing praises to God seven times in it. 737 Lastly, though this same form, starting from the East, has most beneficially spread to these parts, yet still in some long-established monasteries in the East, which will not brook the slightest violation of the old rules of the Fathers, it seems never to have been introduced. 738
The allusion is to the monastery at Bethlehem, where Cassian had himself been educated. See the introduction.215:735
Trinæ confessionis exemplo. The words appear to mean that the three Psalms used at these offices are significant of the Persons of the Holy Trinity. So somewhat similarly Cyprian (on the Lords Prayer) speaks of the third, sixth, and ninth hours being observed as a sacrament of the Trinity.215:736
This second “Mattins” of which Cassian has been speaking is the service which the later Church called Prime, Cassians first Mattins corresponding to Lauds, and his Nocturns, or “Vigiliæ,” to Mattins. Thus the “seven hours” are made up as follows: (1) Nocturns or Mattins, (2) Lauds, (3) Prime, (4) Tierce, (5) Sext, (6 None, (7) Vespers. Compline, it will be noticed, had not yet been introduced. This appears for the first time in the Rule of S. Benedict (c. xvi.), a century later. By its introduction the “day hours” were made up to seven Nocturns belonging strictly to the night, and answering to the Psalmists words, “At midnight will I rise to give thanks to Thee.” Ps. cxix. 62.215:738
The introduction of Prime appears to have been very gradual even in the West, for, though an office for it is prescribed in S. Benedict (c. xix.), yet there is no mention of it in the Rule of Cæsarius of Arles for monks nor in that of Isidore of Seville, and it is omitted by Cassiodorus in his enumeration of the seven hours observed by the monks. After Benedict the next to mention it appears to be Aurelius, a successor of Cæsarius at Arles, and by degrees it made its way to universal adoption in the West. In the Greek Church the office for it is said continuously with Lauds (τὸ ὄρθρον).