Since you believe Jesus is fully human and He was “concieved”, Mary is fully his mother in the biological sense. Thus, if Mary was not without sin, you believe that part of Jesus’ humanity was stained by Mary’s sin. How does that reconcile with your belief that Jesus was fully God and without sin?
The argument of necessity does not work. If God is capable of seeing that Mary is conceived without sin and preserving her from sin (which, of course, he is), then God is equally capable of conceiving Christ’s humanity without sin within a Mary who has sinned.
But more importantly, do you think it more reasonable that God would select as His mate a sinner and imperfect vessel to bear Himself or select one without sin and a perfect vessel to bear Himself?
*** I don’t think his “mate” is the correct concept. God does not mate. Further, God created human beings with the capacity to choose sin. God did not make humans sin, but he gave us the ability to eat of the tree of knowledge. So, who is to say that He would not be born from a woman who had sinned? (I am not saying that Mary was a great sinner by any means…as I said before, Mary is a Saint and blessed through all ages…Catholics tend to be sensitive on this, so please bear in mind that no offense is intended). Also, Christ took on the sins of the world to redeem us…and knew that He would do so prior to the incarnation. So, yes, it is certainly conceivable that Jesus would be born to a women who was not perfect.***
I understand why it might be easier to not think about this (as you admit). But to not think about it and grasp it as a great mystery, denies one the opportunity to have a greater grasp of the mystery of the incarnation itself, the magnitude of the gift God made by sending His Son, and ultimately the Sacrifice of His Passion and Death.
If the Catholic teaching on this is right, then you would be absolutely correct.
RR, your posts are always filled with sincerity of purpose, interest, and probing. This yearning in you is a great blessing and I respectfully ask you to probe this “potential” mystery with an openness of heart and mind in prayer. I’m confident that it will illuminate much Truth and bring you closer to Christ (which is the goal of all of us on this journey).