At that time in Edessa flourished the wondrous Ephraim, and in Alexandria Didymos, who wrote against those who attacked the dogmas of truth. Ephraim, employing the Syrian language, shed beams of spiritual grace. For although he had not tasted Hellenic learning, he refuted the insidious deceptions of the Greeks and exposed the infirmity of every heretical innovation. And when Harmonius, of old, the son of Bardesanes, composed certain songs, mixing his impiety with the sweetness of melody so as to beguile his hearers and lead them to destruction, Ephraim made use of the harmony of melody, mixing it with orthodox theology, and gave his hearers an antidote that was at once delightful and healing. These same songs, even today, make brilliant the feasts of the victorious martyrs.
L. Parmentier and F. Scheidweiler, ed. Theodoret. Kirchengeschichte. 2nd ed. Die griechischen christlichen Schriftsteller 44. Berlin: Akademie Verlag, 1954: 269. Read the entire work in English here.