The doctrine of the Immaculate Conception - the teaching that Our Lady was born without the stain of original sin - is one of those things protestants (and no doubt today many Catholics today) struggle with because it is one of those concepts that reflect the fruits of the Church's inspired meditation on Scripture rather than being something that can be proved directly from Scripture itself.
But when you think about it, it really is a logical conclusion to draw: Mary is, we are taught the second Eve, who fulfills the promise of Genesis 3:15: "and I will put enmity between thee and the woman and her seed; she (he) shall crush thy head and thou shalt lie in wait for her (his) heel" .
And at the Annunciation, the Archangel Gabriel bestows on her the accolade 'full of grace', something impossible if original sin had still prevailed in her, even though she had not been baptised.
Moreover, the teaching can be traced back to the earliest fathers of the Church, such as SS Justin, Iraenaeus and Tertullian.
Wouldn't this be a great feast to make a Holy Day of Obligation once again in Australia!