What does it mean to be truly human? What does it mean for Jesus to have been fully human?
For hundreds of years these questions and many others like them consumed the Church. Is it even possible for God to be human? How could that be? How could the Son of God be anything but God if we want to understand the Trinity? Why, much less how, would God suffer?
I could go on but this is not a theological exploration. Suffice it to say, that unless Jesus was fully human as well as fully God then none of it makes sense. It is mystery and we are unable reason it out because it is mystery. It is truth, revealed to our "puny intellects" as Augustine would say.
Eutychius came into conflict with emperor Justinian who began to believe the teaching that Jesus’s body was incorruptible, not subject to pain, and therefore was not fully human as well as fully God. His resistance to such thought got him exiled until after Justinian's death. But even then, he too struggled with understanding these mysteries, beginning to emphasize the spiritual over the physical, only to return to the understanding of the God-man as whole body and soul, spirit and divinity, words of which are a theological discussion all in their own.
Eutychius, pray that we recognize the truth and to also recognize when we have strayed.
As a result Of this investigation it became evident that in the sayings Of Theodore of Mopsuestia (which are spoken against on all hands) there are contained very many things contrary to the right faith and to the teachings of the holy Fathers; and for this very reason these same holy Fathers have left for the instruction of the Church treatises which they had written against him. For among other blasphemies of his we find that he openly said that God the Word was one [Person] and Christ another [Person], vexed with the passions of the soul and with the desires of the flesh, and that he little by little advanced from a lower to a higher stage of excellence by the improvement of his works, and became irreproachable in his manner of life. And further he taught that it was a mere man who was baptized in the Name of the Father and of the Son and of the Holy Ghost, and that he received through his baptism the grace of the Holy Spirit, and merited his adoption; and therefore that Christ could be venerated in the same way that the image of the Emperor is venerated as being the persona of God the Word. And he also taught that [only] after his resurrection he became immutable in his thoughts and altogether impeccable.
Moreover he said that the union of the Word of God was made with Christ as the Apostle says the union is made between a man and his wife: The two shall be one flesh; and that after his resurrection, when the Lord breathed upon his disciples and said, "Receive the Holy Spirit", he did not give to them the Holy Spirit. In like strain of profanity he dared to say that the confession which Thomas made, when he touched the hands and side of the Lord after his resurrection, saying, "My Lord and my God", did not apply to Christ (for Theodore did not acknowledge Christ to be God); but that Thomas gave glory to God being filled with wonder at the miracle of the resurrection, and so said these words. But what is still worse is this, that in interpreting the Acts of the Apostles, Theodore makes Christ like to Plato, Manichaeus, Epicurus, and Marcian, saying: Just as each Of these were the authors Of their own peculiar teachings, and called their disciples after their own names, Platonists, and Manichaeans, and Epicureans, and Marcionites, just so Christ invented dogmas and called his followers Christians after himself.
-- Letter of Pope Vigilius to Eutychius