St Peter Damian died in 1072, on February 22, the feast of St Peter’s Chair, a very appropriate day for one who spent so much of his life in service to the Church and to the Holy See. When Pope Leo XII made him a Doctor of the Church in 1828, and extended his feast to the general calendar, he was assigned to the day after his death. In the new calendar, St Polycarp of Smyrna was moved to February 23rd, his date in the Byzantine Rite, and Peter Damian was therefore moved to the 21st.
He was born in the early 11th century, an age when the Church in western Europe lay very low indeed. Lay control of ecclesiastical offices and the attendant vice of simony were rampant, and the discipline of clerical celibacy was widely ignored. His youth also saw the appalling spectacle of Pope Benedict IX, whom St Robert Bellarmine called “the nadir” of the Papacy. But even the worst days of the Church’s history are not without their Saints, and 11th-century Italy also saw a new flourishing of reform-minded monastic orders. St Peter Damian was formed as a religious among them, and called to serve as abbot of an important house of the Camaldolese order at Fonte Avellana.
It is truly often darkest before the dawn; after the deposition of Benedict IX and the extremely brief (24 day) reign of Damasus II, the Papal throne was occupied by an active and enthusiastic reformer, St Leo IX (1049-54). Thenceforth, the reform party within the Church was very much in the ascendant, with St Peter Damian as one of its most powerful leaders and spokesmen.
A large part of his voluminous writings consists of exhortations to the clergy at all levels to embrace a stricter and more disciplined life. Three of his letters were regarded as especially important treatises for the reformers of the age, and circulated widely as separate “books.” The “Liber gratissimus” treats of the problem of simony, which he condemns in the harshest possible terms. (“Judas sold the Lord, … but soon thereafter cast away the price of blood… you, on the other hand, … keep the profit from the sacrilege you commit.”) The “Liber gomorrhianus” treats of the worst aspects of sexual immorality among the clergy. The third is known by the odd title “Liber ‘Dominus vobiscum’ ”, and is of particular interest in the field of liturgical history.
It was addressed to a monk and hermit named Leo, who had written him to inquire whether he ought to say “The Lord be with you” and “Pray, lord, give the blessing” when reciting the Divine Office alone. St Peter’s answer is argued at length and with great thoroughness, but what it really boils down to is “the liturgy is not about you.” Since it is the public prayer of the Church, which is made of many members and yet One in the Holy Spirit, the liturgy may rightly speak in the singular in choir (he cites words from the Psalms such as “Incline to me Thine ear, o Lord” and “I will bless the Lord at all times”), and in the plural when celebrated by only one. He also notes, perhaps more persuasively, that a very large part of the Office is written in the plural, invitatories such as “Come, let us worship the Lord”, hymns such as “Rising in the night, let us all keep watch” etc.; so much that to switch it to the singular in private prayer would mean to either omit most of it or mutilate it.
(The Madonna and Child with Ss Anne, Elizabeth, Augustine and Peter Damian, by Ercole Roberti, 1479-81. Executed for the church of Santa Maria in Porto outside Ravenna, now in the Brera Gallery in Milan.)

“Si ergo credentes in Christum unum sunt, ubicumque videatur esse per corporalem speciem membrum, ibi etiam per sacramenti mysterium totum est corpus. Et quidquid est quod competat toti, quodammodo congruere videtur etiam parti: quatenus et quod conventus Ecclesiae communiter sonat, non absurdum sit, si unus homo singulariter dicat: et quod ab uno recte depromitur, a pluribus etiam irreprehensibiliter proferatur. Hinc est enim quod in conventu positi, recte omnes dicimus: ‘Inclina, Domine, aurem tuam, et exaudi me: quoniam egenus et pauper sum ego; custodi animam meam, quoniam sanctus sum.’ Et singulariter constituti, non incongrue decantamus, ‘Exsultate Deo adjutori nostro, jubilate Deo Jacob.’ … Quia nimirum neque hic pluralibus verbis unius personae solitudo praejudicat: neque illic multitudo fidelium a singularitate discordat: quia per virtutem sancti Spiritus, qui et singulis inest, et omnes replet, et hic solitudo pluralis, et illic multitudo intelligitur singularis.
If, therefore, those who believe in Christ are one, wherever there is seen a member according to outward appearances, there also, by the mystery of the sacrament, the whole body is present. And whatever belongs to the whole seems also in some measure to be fitting to the part; so it is not absurd in one man by himself says anything which the body of the Church as a whole utter, and that which is properly said by one person may in the same way be brought forth by many without reproach. It is for this reason that when we are all assembled together, we rightly say, ‘Incline thine ear, o Lord and hear me: for I am poor and needy. Preserve my soul, for I am holy.’ (Ps. 85) And when we are by ourselves, there is no incongruity in our singing: ‘Sing aloud unto God our help: make a joyful noise unto the God of Jacob.’ (Psal. 80) … For surely the solitary condition of one person does no injury to the words in the plural; nor does the multitude of the faithful lack in harmony with the one, since by the power of the Holy Spirit, who is in each, and fills all, on the one hand, the solitude is understood to be plural, and on the other, the multitude to be singular.”