Council of Ephesus (431) — the holy Virgin is Theotokos — English translation from Norman P. Tanner (ed.), Decrees of the Ecumenical Councils, as posted at papalencyclicals.net (official text, quoted at the cited paragraph)
From the second letter of Cyril of Alexandria to Nestorius (read and approved at the Council):
This is the account of the true faith everywhere professed. So shall we find that the holy fathers believed. So have they dared to call the holy virgin, mother of God, not as though the nature of the Word or his godhead received the origin of their being from the holy virgin, but because there was born from her his holy body rationally ensouled, with which the Word was hypostatically united and is said to have been begotten in the flesh.
From the Twelve Anathemas proposed by Cyril and accepted by the Council of Ephesus:
- If anyone does not confess that Emmanuel is God in truth, and therefore that the holy virgin is the mother of God (for she bore in a fleshly way the Word of God become flesh, let him be anathema.
This text is under copyright; the cited paragraph is quoted for study, with a link to the full document. Translation: English translation from Norman P. Tanner (ed.), Decrees of the Ecumenical Councils, as posted at papalencyclicals.net.
Why Pitre cites it
The council approved Cyril's teaching that 'the holy virgin is the mother of God,' and anathematised its denial — the premier case of a belief about Mary resting on a belief about Christ.
Notes
Two extracts. (1) The sentence from Cyril's second letter reads "So have they dared to call the holy virgin, mother of God" (Tanner renders Theotokos as "mother of God", lower-case). (2) Anathema 1 as posted lacks the closing parenthesis after "become flesh"; reproduced as found. The paragraph headings/labels in this entry are editorial.