'"[9]King Sigismund III Vasa's policy for the Counter-Reformation in the Polish–Lithuanian Commonwealth was to reunite, "through missions to non-Catholics, both Protestant and Orthodox," all Christians into the Catholic Church.

[10]: 302–303  After preliminary negotiations with Sigismund III and with Grand Chancellor and Great Hetman of the Crown Jan Zamoyski, a delegation of bishops from the Eastern Orthodox Metropolitanate of Kiev (1458–1596) [uk] was sent to Rome in 1595 to accede to the Union of Brest on condition that their rituals and discipline were left intact.

[11]: 204  The Union resulted in two sectarian groups: He was born Ioann Kuntsevych in 1580 or 1584 in Volodymyr,[g] Volhynian Voivodeship, in the Lesser Poland Province of the Polish Crown (now in Ukraine).

In the school at Volodymyr he gave evidence of unusual talent; he studied Church Slavonic and memorized most of the Horologion, which from this period he began to read daily.

In Vilnius, divided through the contentions of the various religious sects, he became acquainted with men such as Josyf Veliamyn Rutsky, a former Calvinist who converted to Catholicism and transferred from the Western to the Byzantine Rite.

Seeking to emulate the Desert Fathers of Roman Egypt, Brother Josaphat repeated the Jesus Prayer so constantly that he was heard to still murmur it during his sleep.

He also engaged in many acts of mortification of the flesh, such as praying overnight in the parish cemetery during the winter, while barefoot and deliberately underdressed, in order to offer up his suffering towards the salvation of souls.

[19] According the Beatification testimony of his fellow monks, Brother Josaphat regularly prayed while disciplining himself, "Lord, God, grant unity to the Holy Church and the conversion of the Dissidents.

"[20] Stories that the young monk was a Greek Catholic Starets spread rapidly and many distinguished people began to visit the Monastery to speak with him for Spiritual direction.

[21] Brother Josaphat's believed, based on his own studies of history, the liturgical books, and many other sources, that the Union of Brest represented a return to the true roots and origins of the Christian East.

He was so successful at arguing in favor of this point and persuading both Orthodox Christians and Ruthenian and Lithuanian Calvinists to convert to Eastern Catholicism, that his theological opponents dubbed him, "The soul-snatcher".

They painted a picture of the Last Judgement which they placed in the vestibule of the Orthodox church, in which Josaphat was depicted as one of the devils who was dragging souls to Hell with a hook.

'"[24] Whenever Brother Josaphat, however, was called this name, however, he would chuckle and respond, "God grant me the grace to snatch all your souls and lead them to Heaven.

As a result of his efforts, the number of novices to the Order steadily increased, and under Rutsky – who had meanwhile been ordained a priest – a revival of Eastern Catholic monastic life began among the Ruthenians (Belarusians and Ukrainians).

He faced stiff opposition from the monks, who feared liturgical Latinisation of the Byzantine Rite as well as from widowed priests who had remarried in open violation of the Eastern Code of Canons.

As archeparch he: restored the churches: issued a catechism to the clergy, with instructions that it should be memorized; composed rules for priestly life, and entrusted deacons the task of superintending their observance; assembled synods in various towns in the dioceses; and firmly opposed the Grand Chancellor of the Grand Duchy of Lithuania, Lew Sapieha, who wished to make what Josaphat saw as too many concessions to the Eastern Orthodox at the expense of Greek Catholic faithful.

[examples needed] Throughout all his strivings and all his occupations, he continued his religious devotion as a monk, and never abated his practice of mortification of the flesh in order to offer up his sufferings for the conversion of others.

In 1620 they assembled in synod at Kiev, protected by Petro Konashevych-Sahaidachny, hetman of Zaporizhian Cossacks, and elected new Eastern Orthodox bishops including Meletius Smotrytsky as archbishop-elect of Polotsk, all of whom were consecrated "in great secrecy" at Kiev by Theophanes III, the visiting Greek Orthodox Patriarch of Jerusalem, Neophyte, metropolitan of Sofia, and Avramios, bishop of Stagoi.

[clarify][31][failed verification] After 1620, according to Orest Subtelny, in Ukraine, sectarian violence over ownership of church property increased and "hundreds of clerics on both sides died in confrontations that often took the form of pitched battles.

[40]: 263 In January 1624, a commission presided over by Sapieha investigated Kuntsevych's murder and sentenced 93 people to death for their involvement in the conspiracy,[6]: 57 [n] and many were banished and their property confiscated.

Kuntsevych's favourite devotional exercise was the traditional Eastern monastic practice of prostrations, in which the head touches the ground, while saying the Jesus Prayer.

From Kuntsevych's zealous study of the Church Slavonic Byzantine Rite liturgical books he drew many proofs of Catholic doctrine and wrote several original works.

Among his converts were many important personages such as deposed Patriarch Ignatius, of Moscow, and Manuel Kantakouzenos, who belonged to the imperial family of the Byzantine Emperor Palaeologus.

[clarify] After numerous miracles attributed to Kuntsevych were reported to Church officials, Pope Urban VIII appointed a commission, in 1628, to inquire into his possible canonization, which examined 116 witnesses under oath.

[47] During the 1990s, a group of Byzantine Rite Traditionalist Catholic priests and laity, who had survived the underground Church during the 1947-1987 religious persecution by the Soviet Government and the Russian Orthodox Church, founded the Priestly Society of Saint Josaphat in protest against the allegedly modernistic theology and actions of the UGCC hierarchy which had arrived from the Ukrainian diaspora since the collapse of the Soviet Union.