Born at Kenty, a market- town in the diocese of Cracow, St. John was raised up by Providence to keep alight the torch of faith and the flame of Christian charity during the fifteenth century in Poland.
He obtained all the academical degrees at the University of Cracow, where he taught for several years. Ordained priest, he every day offered the Holy Sacrifice to appease heavenly justice, for he was deeply afflicted by the offenses of men against God.
He shone especially by his exquisite charity which is shown in the Introit, the Collects, the Epistle, the Gradual, the Offertory and the Communion of his Mass. He took from his own food to help those who were in need and even gave them his clothes and shoes (Epistle); and he would let his cloak fall to the ground so as not to be seen returning home barefoot. While on a pilgrimage to Rome, he was robbed by brigands, and when he declared that he had no other possession, they allowed him to pursue his journey. The saint, who had sewn some pieces of money in his cloak suddenly remembered this, and calling the thieves he offered them the sum. But they, touched by his goodness and candour, gave him back all that they had taken.
St. John Cantius died on Christmas Eve, A.D. 1473.
He is specially invoked in cases of consumption: "Owing to your prayers we see epidemics disappear, stubborn diseases averted and the blessing of health restored. Those whom consumption, fever and ulcers condemn to a painful end are by you delivered from the embrace of death." (Hymn of Second Vespers)
(Ecclesiasticus 18:12-13 and Psalm 1:1 from the Introit of Mass).
Da, quaesumus, omnípotens Deus: ut, sancti Joánnis Confessóris exémplo in scientia Sanctórum proficiéntes atque áliis misericórdiam exhibéntes; ejus méritis, indulgéntiam apud te consequámur.
Grant, we beseech Thee, almightly God, that by the example of Thy holy confessor John, we may advance in the science of the saints, and show mercy to others, that through his merits we may obtain forgiveness from Thee.
The Roman Breviary has proper hymns for St John Cantius at Vespers, Matins and Lauds. This is a rare honour, and enjoyed by no other confessor who is not a Bishop.
Great John! thou dost a beacon stand
To Poland's folk, to learning's halls,
Thou father of thy fatherland,
Priest-guardian of her Church's walls.
From the Catholic Encyclopaedia: http://www.newadvent.org/cathen/08451b.htm