If not abstaining from flesh-meat on Friday, then what? I have usually followed the advice of Paul VI to either give alms, or to pray. A redoubled focus on prayer on Friday is surely appropriate, given Our Lord's three hour agony on Calvary, when He himself prayed during His great self-offering as our High Priest and Sacrifice.
One sensible choice, then, would be to meditate on His Passion – as by reciting the Fifteen Oes of St Bridget (eminently pious prayers probably composed in mediæval England which ought be disentangled from the superstitious and unapproved promises too often linked with them under the pretext of their attribution to St Bridget of Sweden); or by praying with Our Lord Himself the Passion Psalms (Pss 21:1 to 30:6 inclusive), which mediæval authors conclude He meditated upon as He hung upon the Cross, given their first and last verses being among His Seven Last Words. So, too, attendance at Mass would unite one to the Passion of Christ (as celebrated by some, all too painfully – offer oneself up as a victim soul); as would, at a lesser level, the singing prayerfully of hymns in honour of the Passion, such as the Vexilla Regis.
But Friday is not merely the weekly commemoration of the suffering and death of the Son of God – it is moreover the time for the sons of men to smite their breasts (as once did the mocking crowd at Golgotha as shamefaced they stole away), realizing that it is our sins that impelled Jesus to shed His Blood to save us, and that we Christians who backslide do but recrucify Our Lord.
For this reason, the Penitential Psalms (beloved of St Augustine, who had them written out and affixed to the wall of his bedchamber as he lay dying during the Vandal siege of Hippo) are excellent passages to "read, mark, learn and inwardly digest". However, while praying all seven – Psalms 6, 31, 37, 50, 101, 129 and 142 – is the ideal, mayhap circumstances preclude this: what then?
Now two of the Penitential Psalms are better known (or ought be) than the others: the Miserere (Psalm 50) and the De profundis (Psalm 129), which are par excellence the psalm-prayers of penitence and for the souls in purgatory (where repentant sinners go, ere their penance be complete). I first came across these said together as a devotion in a Monastic Breviary, which prefixed certain verses of Psalm 2, and appended the Collect for Good Friday – the whole being appointed for use while taking the discipline (a practice never to be undertaken without permission of a prudent spiritual director, be it noted!).
Since I have a good memory – which is a real help in the matter of praying the Psalms and indeed of internalizing Scripture, in the hope it may melt the hard heart and engender virtue – I long since learnt those two Psalms by heart. I customarily add to the first the "Glory be" and some preces (threefold Kyrie, Lord's Prayer, versicles and a collect for forgiveness of sins), and to the second "Eternal rest" and some more preces (versicles and the collect Fidelium for the faithful departed). It strikes me that Our Lord prayed for sinners (the living dead) as He died, that they might truly live; and that the merits of His atonement extend to Purgatory also. For this reason, when – as often – I have not the Penitential Psalms easily to hand, I can at least pray these two thereof.
A calculation demonstrates that saying the Miserere and De profundis thrice each, with the usual prayers appended, equates to the whole Seven Penitential Psalms: which I take to be a reasonable and rational measure of suitable prayer for Friday penance. Usually I pray them according to the Vulgate text, but also in English sometimes (I know them in the Grail version, from using the modern Liturgy of the Hours for years), adding these customary preces in the Latin tongue:
Preces for Psalm 50
(after concluding with the Gloria Patri)
Kyrie, eleison. R/. Christe, eleison. Kyrie, eleison.
Pater noster, (secreto) qui es in cælis: Sanctificetur nomen tuum: Adveniat regnum tuum: Fiat voluntas tua, sicut in cælo, et in terra. Panem nostrum quotidianum da nobis hodie: Et dimitte nobis debitas nostra, sicut et nos dimittimus debitoribus nostris.
V/. Et ne nos inducas in tentationem. R/. Sed libera nos a malo.
V/. Salvos fac servos tuos. R/. Deus meus, sperantes in te.
V/. Esto nobis, Domine, turris fortitudinis. R/. A facie inimici.
V/. Nihil proficiat inimicus in nobis. R/. Et filius iniquitatis non apponat nocere nobis.
V/. Domine, non secundum peccata nostra facias nobis. R/. Neque secundum iniquitates nostras retribuas nobis.
V/. Mitte nobis, Domine, auxilium de sancto. R/. Et de Sion tuere nos.
V/. Domine, exaudi orationem meam. R/. Et clamor meus ad te veniat.
Or. Deus, cui proprium est misereri semper et parcere: suscipe deprecationem nostram; ut nos, et omnes famulos tuos, quos delictorum catena constringit, miseratio tuæ pietatis clementer absolvat. Per Christum Dominum nostrum. R/. Amen.
Preces for Psalm 129
(after concluding with Réquiem ætérnam dona eis, Dómine: et lux perpétua lúceat eis.)
V/. A porta inferi. R/. Érue, Dómine, ánimas eórum.
V/. Dómine, exáudi oratiónem meam. R/. Et clamor meus ad te véniat.
Or. Fidélium, Deus, ómnium cónditor et redémptor, animábus famulorum famularúmque tuárum remissiónem cunctórum tríbue peccatórum: ut indulgéntiam, quam semper optavérunt, piis supplicatiónibus consequántur. Qui vivis et regnas per omnia sæcula sæculorum. R/. Amen.
V/. Requiéscant in pace. R/. Amen.