The holy and mighty Synod therefore said that the Only-begotten Son Himself, Begotten by Nature of God the Father, Very God of Very God, Light of Light, Him through Whom the Father hath made all things, came down and was made Flesh and made Man, suffered, rose the third day, and ascended into the Heavens. And these both words and doctrines we too must follow, considering what the Word of God made Flesh and Man means: (For we do not say that the Nature of the Word was changed and made flesh, nor yet that it was changed into whole man, of soul and body: but this rather, that the Word having Personally united to Himself flesh ensouled with reasonable soul unspeakably and incomprehensibly was made Man and was called son of man not in respect of favour only or good pleasure, nor yet by appendage of person only:) and that the natures which are gathered together unto Very Union are diverse, yet One Christ and Son of Both, not as though the diversity of natures were taken away because of the Union, but rather that the Godhead and Manhood make up One Lord and Son through their unspeakable and ineffable coming together into Unity.
This is from what is usually called the Second Letter to Nestorius; it was acclaimed by the Council of Ephesus as sound doctrine, and is a fundamental reference for the orthodox view of the Incarnation.
