The country became renowned across Europe as "a place of shelter for heretics" where anyone could freely profess their faith, even those who denied mainstream Christian doctrines. Faced with the possibility of being thrown into jail or burnt at the stake for dissent from the prevailing faith in their homelands, French, Italians, Czechs and others began to move to the Grand Duchy. In 1557, for example, Duchess Catherine Willoughby of Suffolk and her husband Richard Bertie came to seek asylum in the Grand Duchy due to their Protestant beliefs, by invitation of Mikalai Radzivil the Black.
In January 1573 the Belarusian and Polish nobilities ratified the declaration of the Confederation of Warsaw, which read: "And since there is no small variation in the Christian faith in our republic, warning that no form of hostility should arise between people for this reason, which we see is clearly taking place in other states, we pledge to ourselves, for ourselves and our descendants for all time to preserve peace between us and not, on account of differences in faith, to shed blood in the churches or to deprive anyone of property or social standing, or to subject anyone to arrest or banishment, or to assist any authorities or government in such actions."
The 1588 Statute of the Grand Duchy of Lithuania reiterated the principle of religious freedom. For Europe, enflamed by religious wars, the Confederation of Warsaw became a model of how to resolve issues of freedom of conscience. Writing in his diary at the beginning of the seventeenth century, Belarusian Calvinist nobleman Fyodor Yevlashovsky recalled that: "In Vilnius I sat at the table of [Catholic canon] Fr Bartholomew Nedvitsky, together with his Italian servants. When they found out that I was an evangelical Christian, they were astounded at how it was that a canon priest dared invite me to dinner. And when I told them that no hatred arises between us because of that, and we get along as good friends, the Italians praised this, saying that God lives here, and began to lament the laws in their own land - or rather lawlessness. At that time difference in faith was not a reason for any kind of difference in friendship, and so that age seems to me a golden one, because now untruth exists between people of the same faith, to say nothing about those of different faiths, and you can forget about charity or sincerity."
Yevlashovsky's complaints about the seventeenth century are not without foundation. The accession of Sigismund Vasa to the throne marked the end of religious freedom in the Grand Duchy. Aiming to destroy the Reformation there, the king doggedly pursued all means of ridding the Polish-Lithuanian Commonwealth of everything non-Catholic.
King Sigismund overtly flouted the provisions of the Confederation of Warsaw and restricted the rights of those who did not share the prevailing faith. Mass emigration of non-Catholics resulted, including Orthodox believers who refused to become Eastern-rite Catholics under the 1596 Union of Brest. The lack of religious freedom led to other states benefiting from the migrants' talents and labour. Belarusian émigrés such as Simeon of Polotsk and Yan Belobotsky brought Russia into closer contact with western civilisation. Religious persecution forced Ilya Kopiyevich, a student of
the Calvinist high school in Slutsk, to flee to the Dutch Republic - another state famed for its religious freedom - where he devised a simplified Cyrillic orthography.
