From Dom Guéranger's The Liturgical Year.
PETER and Paul still hear the prayer of their devout clients throughout the world. Time has wrought no change in their power; and in heaven no more than formerly on earth can the gravity of the general interests of holy Church so absorb them, as that they should neglect the petition of the humblest inhabitant of the glorious city of God, of which they were constituted, and still are, the princes. Putting to sleep the faith of even just men is one of the triumphs of hell at present; hence we must be allowed to insist somewhat on our point, in order to disturb this dangerous slumber, which would end in nothing less than the utter oblivion of the most touching consideration of our Lord's intention, when he confided to mere men the continuance of his work and the representation of his Person visibly here below.
The error whereby the world has been turned away from Peter will be decidedly overcome only when it is brought to see in him, not merely the firmness of the rock in resisting the attacks of hell’s gates, but likewise that tenderness of heart and that paternal solicitude which make him to be indeed the Vicar of Jesus in his love. For, in fact, the Church is not merely an edifice, the duration of which is eternal: she is moreover a family, a sheepfold; and therefore our Lord, wishing to leave to his work a triple guarantee when quitting this world, exacted of the chosen one, to whom he would confide all, a triple affirmation of love before investing him with this sublime office, saying: 'Feed my sheep.'
Hence, exclaims St Leo, far from us all doubt as to whether Peter still exercises this function of shepherd, or whether he remains faithful to the engagement he once plighted of an eternal love, or whether he still observes with exquisite tenderness that command of our Lord, to confirm us in good by his exhortations, to pray ceaselessly, lest any temptation prevail against us. His tenderness embraces the whole people of God; it is far more vast and potent now than when he was in this mortal state; because now all the duties and multiplied solicitudes of his immense paternity do him honour, through him with whom and by whom he hath been glorified.
If in every place, again says St Leo, the martyrs have received, in recompense for their death and in manifestation of their merits, the power to aid those in peril, to drive away diseases and unclean sprits, and to cure countless evils; who could be so ignorant or so envious of the glory of blessed Peter as to suppose that any portion of the Church can escape his care, or must not be indebted to him for its progress? Ever burning, ever living, in the prince of the apostles, is that love of God and of men which nothing could daunt; neither chains, nor the straitness of dungeons; neither the fury of mobs, nor the wrath of kings; victory has not cooled that which battle could not conquer. Wherefore in these days, seeing that sorrow has given place to joy, labour to repose, discord to peace, we recognize in these helpful effects the merits and prayers of our Head. Oftentimes do we experience how he influences salutary counsels and just judgements; the right of binding and loosing is exercised by us, but to blessed Peter is due the inclining of the condemned to penitence, of the pardoned to grace. Yea, this which we have personally experienced, our forefathers knew also; in such sort, that we believe and hold for certain, that in all the troubles of this life, the apostolic prayer must be our special aid and safeguard before the throne of God’s mercy.
St Ambrose, bishop of Milan, in his turn also extols the apostolic action ever efficacious and living in the Church. His exposition, so full of sweetness and always so sound, rises to the sublime, wherein his great soul soars at ease, when he comes to express with ineffable delicacy and depth the special role of Peter and Paul in the sanctification of the elect.
The Church, he says, is the ship in which Peter must fish; and in this toil he is sometimes to us the net and sometimes the hook. O great mystery! for this fishing is wholly spiritual. The net encloses, the hook wounds; but into the net go the crowd; unto the hook go the solitary fish. Do not, therefore, O good fish, dread Peter's hook; it killeth not, but consecrateth; his is a precious wound, midst the blood of which may be found the coin of good metal, needed to pay tribute both for the apostle and for the Master. Hence, undervalue not thyself, for though thy body be feeble, in thy mouth thou hast wherewith to pay both for Christ and for Peter. Lo! within us is a treasure, the Word of God; by being confessed, Jesus is placed upon our lips. Wherefore is it said to Simon: “ Launch out into the deep,"—that is to say, into the heart of man; for the heart of man in his counsels is as deep water. Launch out into the deep—that is, into Christ—for Christ is the fountain of living waters, in whom are the treasures of wisdom and knowledge. Daily still doth Peter preach; daily the Lord crieth unto him: “Launch out into the deep." But methinks I hear Peter answer him: “Lord, we have laboured all the night, and have taken nothing." Peter toils in us when our devotedness is laborious. Paul, too, is in labour; even this very day have ye not heard him saying: “ Who is weak, and I am not weak?" So behave, that the apostles may not have to toil thus hard for you.
The Ambrosian Missal offers us the following Preface and Prayer for this feast:
Æquum et salutare: nos tibi semper, hic et ubique, in honore apostolorum Petri et Pauli gratias agere.. Quos ita electione tua consecrare dignatus es: ut beati Petri sæcularem piscandi artem in divinum dogma converteres, quatenus humanum genus de profundo inferni præceptorum tuorum retibus liberares; et coapostoli ejus Pauli mentem cum nomine mutares, ut quem prius persecutorem metuebat Ecclesia, nunc cœlestium mandatorum lætetur se habere doctorem. Paulus cæcatus est, ut videret: Petrus negavit, ut crederet. Huic claves cœlestis imperii: illi ad evocandas gentes, divinæ legis scientiam contulisti. Ille introducit; hic aperit: et ambo virtutis æternæ præmia sunt adepti. Hunc dextera tua gradientem in elemento liquido, dum mergeretur, erexit; illum autem, tertio naufragantem, profunda pelagi fecit vitare discrimina. Hic portas inferi, ille mortis vicit aculeum: et Paulus capite plectitur, quia gentium caput fidei probatur; Petrus autem, sursum versis vestigiis, caput omnium nostrum secutus est Christum.
It is truly meet and just for us here and everywhere to give thanks in honour of the apostles Peter and Paul. Whom thou hast vouchsafed to consecrate by such an election: so that the earthly fishing-craft of blessed Peter should be converted by thee into divine dogma, inasmuch as thou hast been pleased to deliver the human race from the depths of hell, by means of the nets of thy commandments; and that the mind of his co-apostle Paul, as well as his name, should be changed by thee, so that he who at first was dreaded by the Church, should now make her gladsome by the teaching of the heavenly precepts which he hath received. Paul was struck blind, in order that he might see; Peter denied, in order that he might believe. To the one belong the keys of the heavenly kingdom: to the other thou hast entrusted the knowledge of the divine Law, that he might call the Gentiles to the faith. The one introduces; the other opens; and to both is awarded the prize of eternal dominion. The one, as he walked upon the waters, was upheld by thy right hand when about to sink: the other, thrice shipwrecked, was by the same saved from the depths of the sea. The one resists the gates of hell; the other overcomes the sting of death: and Paul has his head struck off, because he is the approved head of the nations in faith; but Peter, with his feet turned heavenwards, hath followed Christ the Head of us all.
Deus, qui confitentium tibi redemptor es animarum, quarum piscator beatus Petrus apostolus, atque ovium pastor tua præceptione cognoscitur: annue misericors precibus nostris, et populo tuo pietatis tuæ dona concede. Qui vivis.
O God, the Redeemer of souls confessing unto thee; of souls caught by thy fisherman, blessed Peter the apostle; of sheep unto whom, according to thy command, he is known to be the shepherd: be pleased, in thy mercy, to grant our petitions; and to thy people, vouchsafe the gifts of thy compassion. Who livest.
Let us hail Rome and her two princes in the words of this beautiful song, which breathes something of the inspiration found in the hymns of Elpis and of St Paulinus of Aquileia. It is supposed to date from about the seventh or eighth century.
O Roma nobilis, orbis et domina,
Cunctarum urbium excellentissima,
Roseo martyrum sanguine rubea,
Albis et virginum liliis Candida:
Salutem dicimus tibi per omnia,
Te benedicimus, salve per sæcula.
Petre, tu præpotens cœlorum claviger,
Vota præcantium exaudi jugiter:
Cum bissex tribuum sederis arbiter,
Factus placabilis judica leniter,
Teque precantibus nunc temporaliter
Ferto suffragia misericorditer.
O Paule, suscipe nostra peccamina,
Cujus philosophos vicit industria:
Factus œconomus in domo regia,
Divini muneris appone fercula;
Ut, quæ repleverit te Sapientia,
Ipsa nos repleat tua per dogmata.
O noble Rome, O lady of the earth,
O most excellent of all cities,
ruddy with the roseate blood of martyrs,
and white with the glistening lilies of virgins:
we salute thee throughout the earth:
we bless thee; for ever, hail!
O Peter, thou most potent key bearer of the heavens,
meetly hear the prayers of us suppliants:
when thou dost sit as judge of the twelve tribes,
being appeased, judge us mildly;
and now whilst time is still ours, mercifully lend thine intercession
unto us who are beseeching thee.
O Paul, take in hand the cause of us guilty ones,
thou whose skill did conquer philosophers:
being made dispenser in the royal household,
hand unto us the sweetmeats of divine gifts;
so that the same Wisdom that filled thee
may replenish us by thy teachings.
 Ambr. in Luc. x.
 St John xxi.
 Sermo IV de Natali ipsius.
 Sermo III de Natali ipsius.
 Sermo V de Nat. ips.
 Sermo I in Nat. Apost.; lect. II Noct. quintæ diei infra Oct.
 De Virginitate xviii.
 St Matt. xvii 23-26.
 Ambr. Hexæmeron, V.
 St Luke v 4.
 Prov. xviii 4.
 St John iv 11.
 Rom. xi 33.
 St Luke v. 5.
 2 Cor. xi 29.
 Ambrosius de Virginitate xviii, xix. This portion of the Book on Virginity forms a part of a discourse which was delivered by St Ambrose on the festival of the holy apostles. In the Ambrosian liturgy, there is still read, for the Epistle of this feast, the passage containing the text cited above by St Ambrose, from the Epistle of St Paul to the Corinthians.