We can describe our spiritual evolution as a journey from the unconscious unity to the conscious unity. The serpent holding its own tail is the symbol of unconscious unity. It is sinless state but unconscious like small children before self-consciousness. We can describe this state as original blessing. It is the experience of Garden of Eden before the fall.
The serpent crawling on the ground is the symbol of ego, time, becoming, effort, sin, struggle, good and evil, duality, separation. It is coming out of the Garden of Eden and original blessing and taking the path of becoming and sin.
The serpent raising its hood is the symbol of conscious unity. It is reentering into the Garden of Eden but consciously. It is rediscovering our original blessing. It is like the prodigal son who comes out the original blessing- experiences the path of sin and returns back to the original blessing consciously.
If we see the statue of Mary, we see a serpent under her foot. This serpent is the symbol of becoming, ego, good and evil, fragmented self, psychological time. In Hinduism and Buddhism, they call it samsara, the movement of ignorance and desire and karma. Mary is the symbol of human consciousness which stops this movement and gives birth to incarnation, enlightenment and freedom.
Jesus Christ also had to encounter this serpent crawling on the ground and not to submit it. He also stops it and realizes oneness with God.
There is no direct path from the unconscious unity to the conscious unity, except by the special grace of God. Every one has to enter the second level, to eat the forbidden fruit and then come back to the original blessing.
I have no difficulty to accept if Mary and Jesus also have passed that level. So that they can be real models for every human being. If they were given a special grace then they stand above other human beings and create spiritual apartheid.
Sin belongs to the evolutionary process of our human consciousness. It is a necessary process. We cannot bypass it. We all need to grow through it. That is why St.Paul says that everyone has committed sin. But we have also the possibility to rise about it.