Sinlessness is the human nature. Let us recall that sinless Christ is fully human. Immaculate conception in no way denies Mary her humanity. Rather, our sin denies ours.
"Sinlessness is the human nature. Let us recall that sinless Christ is fully human. Immaculate conception in no way denies Mary her humanity. Rather, our sin denies ours."
Now you see, I don't believe at all that sinlessness is human nature except to this extent. Our created purpose was to be in both the image and likeness of God. To the extent that that can be attained, then our created purpose has been fulfilled and since we would be in union with the uncreated energies of God, we would therefore be sinless. Adam and Eve were not created perfect. They were created with potential, a potential they lost for themselves and us through the Sin and which Christ restored. Human nature became distorted through that Sin and lost the potential to attain theosis. This is not to say that the Theotokos couldn't have remained sinless through her entire life up to the resurrection. I believe she did. But without that resurrection, she could not have attained theosis because as a child of Adam, she was bound by death as a consequence of Adam's Sin. On the other hand, if she was conceived with no effect of the sin of Adam in her, then she wasn't bound by the bonds of death, she wasn't human the way the rest of us are and she didn't need a savior. Under this line of thinking, she might well be the "Co-Redemptrix" and Christ, born of her, might not be True Man. But that's not Orthodoxy.