Episcopal Labors and Enlightenment of Rostov
When Isaiah came to Rostov, the Christian faith had not yet taken firm root in the region, and much of its population remained pagan. The synaxarion relates that he traveled through his diocese preaching the Gospel, overturning idols, and encouraging the spread of Christianity among the people. The Russian sources name an extensive territory under his oversight, including the lands later associated with Yaroslavl, Vladimir, and surrounding regions.
By tradition, an angel miraculously transported Saint Isaiah to the Kiev Caves Lavra so that he might take part, together with the metropolitan and other bishops, in the consecration of the great Dormition church there in 1089. This episode, recounted in his life as a sign of his sanctity, is one source of his title as wonderworker.