Notwithstanding his literary activity, Theodore worked zealously for the good of his diocese. The famous letter of Ibas to Maris testifies that he struggled against extinguished Arianism and other heresies in Mopsuestia. Several of his works are doubtless monuments of these pastoral labors, e.g. the catechetical lectures, the "ecthesis," and possibly the treatise on "Persian Magic." Yet his episcopal work was by no means simply that of a diocesan bishop. Everywhere he was regarded as "the herald of the truth and the doctor of the church"; "even distant churches received instruction from him." So Ibas explained to Maris, and his letter was read without a dissentient voice at the Council of Chalcedon (Facund. ii.i seq.). Theodore "expounded Scripture in all the churches of the East," says John of Antioch (ibid. ii.2), with some literary license, and adds that in his lifetime Theodore was never arraigned by any of the orthodox. But in a letter to Nestorius (ibid. x.2) John begs him to retract, urging the example of Theodore, who, when in a sermon at Antioch he had said something which gave great and manifest offence, for the sake of peace and to avoid scandal, after a few days publicly corrected himself. Leontius tells us that the cause of offence was a denial to the Virgin Mary of the title Theotokos. So great was the storm that the people threatened to stone the preacher (Cyril of Alexandria Ep. 69). The heretical sects attacked by Theodore showed their resentment in a way less overt, but perhaps more formidable. They tampered with his writings, hoping thus to involve him in heterodox statements (Facund. x.1).