Q. Isn’t being sinful part of our fallen human nature? If so, how can we say that Jesus was “fully human” if He never sinned?
A. When our first parents fell from grace, they damaged the human nature that God had created for them. It became disordered, twisted, broken. Consequently, they could not pass on to their descendants what they themselves no longer possessed. The original sin that now affects all of us is thus a deficiency in human nature, a lack of the original righteousness with which the human race was created.
In this light, then, we come to see that it is precisely Jesus’ sinlessness that makes Him fully human. In His perfect, unfallen human nature, He is the kind of human being that God originally intended. Nothing is lacking in His human nature, nothing damaged or diminished by sin.
On the other hand, because we are sinners, we are actually to one extent or another less than fully human. You and I have not, in this life, attained to the full human perfection for which God has created us.
God willing, we will one day reach that full perfection of humanity when we stand before Him in heaven, enjoying the Beatific Vision. Then we too will be “fully human”! PT