PROOF OF THE IMMACULATE CONCEPTION
A good sister asked for proof of the validity of the immaculate
conception dogma.
We briefly replied :

Evidence is simply that God dwells in the holiest of places and if
he ever came into the womb of Mary (which he did), he must
have prepared it free from every stain of sin. Her womb, like
heaven became unstained with even the slightest taint of original
or actual sin.
Again if Jesus were to save us from sin, he too would not be
affected by original sin. If Mary were affected by original sin,
then Christ too would have suffered this too and would therefore
be unable to save Us since he himself would be in this sin with
us. However if Christ would save he needed be outside this pit
of sin to draw us away from it. And Mary's immaculate
conception was a way for Christ to be free from this sin and be
in good position to draw us from it.
Plus, he also has revealed this truth to the Church over the
years. I hope this suffices. God bless you.
How Can Anybody But Christ Be Sinless? Doesn't Mary Need
a Savior Too?
Only Christ is sinless on his own account. Mary was rendered
sinless on account of a prevenient action of God, applying
Christ's future merits and perfection to her. Mary did no work
to make her a sinless vehicle for God-in-the-flesh. It was
purely on account of God's grace, and the work of Christ, that
Mary was made sinless.
Yes, Mary needed a savior. And Christ was an amazing savior
to his mother, because through his merits as savior of
mankind, God redeemed Mary in a most remarkable manner,
preserving her from the stain of Original Sin. In fact, in
Scripture Mary rejoices in the wonderful work of her savior,
connecting her salvation in Christ with all generations calling
her blessed:
My soul proclaims the greatness of the Lord, my spirit
rejoices in God my savior.
For he has looked with favor on his lowly servant:
From this day all generations will call me blessed
(Matthew 1:46-48).
Doesn't This Feast Emphasize Mary Too Much?
The Opening Collect for the Mass on the Feast of the
Immaculate Conception begins: "Father, You prepared the
Virgin Mary to be the worthy Mother of Your Son..." As this
prayer emphasizes, the Immaculate Conception is not so much
about honoring Mary, but making Mary a worthy bearer of God
the Son in the flesh. The Church, East and West, has always
held that Mary was no ordinary mother, but the Mother of
Jesus Christ, true God and true Man. With this comes special
graces and honors, not on account of who Mary is per se, but
on account of who her Son is.