Blessed Stanislaus Papczynski (1631-1701), founder of the Marians of the Immaculate Conception, which now has more than 500 priests in 19 countries, promoted social justice and prayers for the dying.
In a pastoral letter read in churches the last weekend in May, Polish bishops said Blessed Papczynski showed "the path to salvation is not closed to any sinner who is open to repentance."
They said Father Papczynski had created the order when his country was "sunk in endless war, famine and disease," after realizing that many Poles, soldiers included, were dying "unprepared for meeting with God."
"Father Papczynski showed that love is the spirit, light and life of every order and social community, that no needy person should be left to die without support," they said.
The Polish bishops said Blessed Papczynski had established clinics and shelters for the "distressed, rejected and unjustly treated," and to counter the alcoholism, rampant in the 17th century.
They said the saint had encouraged charity "out of love for God and man, as well as love of homeland," and had stressed that "God's mercy always comes first and surpasses our sins."
"Father Stanislaus summons us today as he did 300 years ago to remember true freedom comes from observing divine rules before human ones," the bishops' conference said.
Born into a blacksmith's family at Podegrodzie, in Poland's southern Beskidy region, Blessed Papczynski joined the Spanish-based Piarist congregation in 1654, after being educated at Jesuit colleges, and became its first full Polish member two years later.
Ordained in 1661, he left the Piarists after nine years, complaining about their lack of rigor, and in 1673 founded a retreat house at Skierniewice for his new Marian order, with a mission to promote the Immaculate Conception and pray for souls in purgatory.
He later served as a military chaplain against Turkish invaders in Ukraine and acted as confessor to King Jan Sobieski during his victory over the Turks at the 1683 Battle of Vienna.
He died at Gora Kalwaria, near Warsaw, and was buried in the Marian church of the Blessed Virgin. He was beatified at the Marian shrine of Lichen in September 2007.
The June 5 canonization will be followed on giant TV screens by pilgrims at Lichen.