From Dom Guéranger's The Liturgical Year.

It is from a court that we are to be taught to-day the most heroic virtues. Casimir is a prince; he is surrounded by all the allurements of youth and luxury; and yet he passes through the snares of the world with as much safety and prudence, as though he were an angel in human form. His example shows us what we may do. The world has not smiled on us as it did on Casimir; but how much we have loved it! If we have gone so far as to make it our idol, we must now break what we have adored, and give our service to the sovereign Lord, who alone has a right to it. When we read the lives of the saints, and find that persons who were in the ordinary walks of life practised extraordinary virtues, we are inclined to think that they were not exposed to great temptations, or that the misfortunes they met with in the world made them give themselves up unreservedly to God’s service. Such interpretations of the actions of the saints are shallow and false, for they ignore this great fact, that there is no condition or state, however humble, in which man has not to combat the evil inclinations of his heart, and that corrupt nature alone is strong enough to iead him to sin. But in such a saint as Casimir we have no difficulty in recognizing that all his Christian energy was from God, and not from any natural source; and we rightly conclude that we, who have the same good God, may well hope that this season of spiritual regeneration will change and better us. Casimir preferred death to sin. But is not every Christian bound to be thus minded every hour of the day? And yet, such is the infatuation produced by the pleasures or advantages of this present life, that we every day see men plunging themselves into sin, which is the death of the soul; and this, not for the sake of saving the life of the body, but for a vile and transient gratification, which is oftentimes contrary to their temporal interests. What stronger proof could there be than this, of the sad effects produced in us by original sin? The examples of the saints are given us as a light to lead us in the right path, let us follow it, and we shall be saved. Besides, we have a powerful aid in their merits and intercession: let us take courage at the thought that these friends of God have a most affectionate compassion for us their brethren, who are surrounded by so many and great dangers.

The Church, in her liturgy, thus describes to us the virtues of our young prince:

Casimirus, patre Casimiro, matre Elisabetha Austriaca, Poloniæ regibus ortus, a pueritia sub optimis magistris pietate, et bonis artibus instructus, juveniles artus aspero domabat cilicio, et assiduis extenuabat jejuniis. Regii spreta lecti mollitie, dura cubabat humo, et clam intempesta nocte, præ foribus tempiorum pronus in terra divinam exorabat clementiam. In Christi contemplanda Passione assiduus, Missarum solemniis adeo erectain Deum mente solebat adesse, ut extra se rapi videretur.

Catholicam promovere fidem summopere studuit, et Ruthenorum schisma abolere; quapropter Casimirum patrem induxit, ut legem ferret, ne schismaticinova templa construerent, nec vetera collabentia restaurarent. Erga pauperes et calamitatibus oppressos benefieus et misericors, patris et defensoris egenorum nomen obtinuit. Virginitatem, quam ab incunabulis servavit illæsam, sub extremo vilæ termino fortiter asseruit, dum gravi pressus infirmitate, mori potius, quam castitatisjacturam ex medicorum Consilio subire, constanter decrevit.

Consummatus in brevi, virtutibus et meritis plenus, prænuntiato mortis die, inter sacerdotum, et religio sorum choros spiritum Deo reddidit, anno setatis vigesimo quinto. Corpus Vilnam delatum multis claret miraculis. Etenim, præterquam quod puella defuncta vitam, cæci visum, claudi gressum, et varii infirmi sanitatem ad ejus sepulchrum recuperarunt. Lithuanis exiguo numero ad potentissimi hostis insperatam irruptionem trepidantibus in aere apparens, insignem tribuit victoriam. Quibus permotus Leo decimus, eumdem sanctorum catalogo adscripsit.

Casimir was the son of Casimir, king of Poland, and of Elizabeth of Austria. He was put, when quite a boy, under the care of the best masters, who trained him to piety and learning. He brought his body into subjection by wearing a hair-shirt, and by frequent fasting. He could not endure the soft bed which is given to kings, but lay on the hard floor, and during the night, he used privately to steal from his room, and go to the church, where, prostrate before the door, he besought God to have mercy on him. The Passion of Christ was his favourite subject of meditation; and when he assisted at Mass, his mind was so fixed on God, that he seemed to be in one long ecstasy.

Great was his zeal for the propagation of the Catholic faith, and the suppression of the Russian schism. He persuaded the king, his father, to pass a law, forbidding the schismatics to build new churches, or to repair those which had fallen to ruin. Such was his charity for the poor and all sufferers, that he went under the name of the father and defender of the poor. During his last illness, he nobly evinced his love of purity, which virtue he had maintained unsullied during his whole life. He was suffering a cruel malady; but he courageously preferred to die, rather than suffer the loss of his chastity, whereby his physicians advised him to purchase his cure.

Being made perfect in a short space of time, and rich in virtue and merit, after having foretold the day of his death, he breathed forth his soul into the hands of his God, in the twenty-fifth year of his age, surrounded by priests and religious. His body was taken to Vilna, and was honoured by many miracles. A young girl was raised to life at his shrine; the blind recovered their sight, the lame the use of their limbs, and the sick their health. He appeared to a small army of Lithuanians, who were unexpectedly attacked by a large force, and gave them the victory over the enemy. Leo X. was induced by all these miracles to enrol him among the saints.

Enjoy thy well-earned rest in heaven, O Casimir! Neither the world with all its riches, nor the court with all its pleasures, could distract thy heart from the eternal joys it alone coveted and loved. Thy life was short, but full of merit. The remembrance of heaven made thee forget the earth. God yielded to the impatience of thy desire to be with Him, and took thee speedily from among men. Thy life, though most innocent, was one of penance, for knowing the evil tendencies of corrupt nature, thou hadst a dread of a life of comfort. When shall we be made to understand that penance is a debt we owe to God, a debt of expiation for the sins we have committed against Him? Thou didst prefer death to sin; obtain for as a fear of sin, that greatest of all the evils that can befall as, because it is an evil which strikes at God Himself. Pray for as daring this holy season, which is intended as a preparation for penance; impress our minds with the truths now put before us. The Christian world is honouring thee to-day; repay its homage by thy blessing. Poland, thy fatherland, once the bulwark of the Church, which kept back the invasion of schism, heresy, and infidelity, beseeches thy prayers.