Explanation of the Prayers and Ceremonies of Holy Mass, Dom Prosper Guéranger - Epistle

 After the Collect, and the other Prayers, which are frequently added under the name of Commemorations, there follows the Epistle, which is, almost always, taken from the Epistles of one or other of the Apostles, although, occasionally, from some other Book of the holy Scriptures.  The custom of reading only one Epistle in the Mass, is not of the number of those which were in use in the primitive Church; yet it dates back at least a thousand years.  In the Early Ages, there was read, first, a Lesson from the Old Testament; after which, followed some passage selected from the Apostolic Writings.  At present, it is the Epistle alone that is read, excepting on Ember Days and certain Ferias.  The practice of reading Lessons from the Old Testament during Mass, ceased when the Missal was drawn up in its present form, and which contains the whole of what is said at Mass, both by the Priest and by the Choir; and, on that account, is called a Full Missal.  An Ancient Missal, called a Sacramentary, contained nothing, as we have already stated, beyond the Prayers, the Prefaces, and the Canon.  All the rest was to be looked for in the Antiphonary, the Bible, and the Evangeliarium.  We have been losers by the change; for each Mass had its proper Preface; whereas, now, the number of these liturgical compositions is reduced to a minimum.  The same method was observed in the Divine Office, since, in those times, there were no Breviaries; and each Choir had to be supplied with a Psaltery, Hymnary, Bible, Passional, which related the Acts of the Saints, and a Homily-Book, which contained the Sermons of the Holy Fathers.

For a long period after that, the first Sunday of Advent retained its privilege of having two Epistles in the Mass.  At last, it, also, was to have but one.  The Office of this Sunday was, however, treated with a special consideration, and has retained, more faithfully than most others, the ancient usages.  Thus, though a semidouble, the Suffrages are not to be said upon it; nor, indeed, during the whole period up to the Epiphany.  The Suffrages do not date beyond the 11th century; previously there were none.

Thus everything in the holy Sacrifice proceeds with order: the Priest has, first of all, expressed the desires and petitions of the assembled Faithful, - holy Church has spoken through him.  We shall soon be hearing the words of our divine Master, in the Gospel; but we are to be prepared for that, by the word of his servant; this was done in the Epistle.  So that, we first have the Prophet, then the Apostle, and, at length, our Lord Himself.