Feast of the Immaculate Conception

Under Roman Catholic Dogma, the Church has set aside this day to honor the conception of the Virgin Mary without any stain (macula in Latin) of original sin.

And you shall make the ark of testimony of incorruptible wood, and you shall gild it with pure gold, you shall gild it within and without; and you shall make for it golden wreaths twisted round about.
—Exodus 25:10-11 Brenton LXX

Moses used this wood because it was regarded as very durable and "incorruptible". Mary is regarded by Catholic Christians as being the Ark of the Covenant(the new ark - holding Jesus, the new covenant) in the New Testament and therefore claim it is fitting that the New Ark likewise be made "incorruptible" or "immaculate". Their basis for calling the Virgin Mary the Ark of the Covenant is based partly on the parallels of the Ark in Second Samuel 6 with the Nativity narrative of the Gospel of Luke. The early Church Fathers called Christ, the Church, and the Virgin Mary each at one point as being symbolized by the Ark.

It is also claimed that Mary is shown as being totally faithful to Christ, especially during his Passion, when he was abandoned by his followers and apostles except for the young John. In this way, Mary's complete faithfulness is argued to be the fruit of being sinless, as she could not then reject Christ in the darkest hour.~ Wikipedia