Episcopate and the Defense of Orthodoxy
The sources present Theodore's episcopate as chiefly a teaching ministry directed against heresies the synaxarion names as the Arian, Nestorian, and Eutychian errors then present in the region. His diplomatic journey to the Muslim capital is framed as an effort to secure protection for the Orthodox of Edessa rather than as a strictly doctrinal dispute.
By tradition the ruler he met at Baghdad, healed of a grave illness, accepted Christian baptism together with several companions and took the name John; the account further relates that these converts later confessed their faith openly and died as martyrs.