Complex sentence: Jedrzej, Bishop of Vilna, called "Vasilo" by the Lithuanians, truly an apostolic shepherd in the days of King Władysław II Jagiełło, in 1399 preached the Christian faith in Lithuania, at that time still unconverted.
Split into simpler sentences: Jedrzej, Bishop of Vilna, called "Vasilo" by the Lithuanians, was truly an apostolic shepherd in the days of King Władysław II Jagiełło. In 1399, he preached the Christian faith in Lithuania, at that time still unconverted.