Invicti Athletae §11

¹¹ But the Catholic Church, particularly in the countries to the East, was facing an extremely grave crisis owing to the efforts of the schismatics, who were striving by every device to draw the faithful away from the unity of the Church into their own errors. Andrew went, therefore, into those regions on the instruction and command of his Superiors, and by public sermons and private instruction through their cities, towns, and villages, and most of all by the fervor of his exceptional holiness and the burning zeal of his apostolate, he freed the wavering faith of a multitude of Christians from beguiling falsehood, brought them back to sound principles, and joyfully invited all he could to return to the one fold of Jesus Christ.