By Luke Lancaster
Scripture and Tradition is how Catholics arrive at an understanding of all supernatural truths. One of these truths that is particularly contested by non-Catholics is that Mary is all-holy or "Immaculately Conceived." This spiritual belief states that Mary was preserved from all sin: both original and personal. She was set aside by God to be used as the perfect instrument of Christ's presence into the world. There are allusions to this teaching in Scripture (an implicit teaching), but is only understood through the explicating lens of Tradition.
Now, let's remember our articles on the idea of development. With certain teachings passed on by the bishops from the earliest centuries, the understanding of those teachings developed upon further reflection. The teaching of the Immaculate Conception of Mary developed from a kind of "seedling" form, first from the understanding of Mary's immense holiness and purity, then to her being so holy and pure that she committed no personal sins, and finally to the point that she was preserved even of original sin.
This understanding of Mary being immensely holy and pure is due to the association between the Ark of the Covenant or the Holy of Holies with Mary. See a video here. The Ark was overlaid with gold and dwelled inside the golden and sacred Holy of Holies in King Solomon's Temple. It was there that God's presence dwelled, and where only the high priest could enter once a year. In fact, the room was so sacred, that sometimes the priests would die while ministering so close to God Himself (Lev. 10:1-2)! Or if somebody touched the Ark of the Covenant, they died (2 Sam. 6:7)!
From the earliest days of the Church, Mary was seen as a type of the Tabernacle's/Temple's Holy of Holies, or as a type of the Ark of the Covenant. This was because she alone was overshadowed by God's presence - and to the point of giving birth to God Himself - Jesus. If Mary was associated with these holy places/objects, then it is rather understandable why this understanding of Mary being "Immaculately Conceived" developed.
See below the pattern of development:
Hippolytus (c. 170-235) wrote: "At that time, the Saviour coming from the Virgin, the Ark, brought forth His own body into the world from that Ark, which was girded with pure gold within by the Word, and without by the Holy Ghost; so that the truth was shown forth, and the Ark was manifested...He was the ark formed of incorruptible wood. For by this is signified that His tabernacle was exempt from putridity and corruption" (On Daniel 6).
Origen of Alexandria (c. 184-254) wrote: “This Virgin Mother of the Only Begotten of God, is called Mary, worthy of God, immaculate of the immaculate, one of the one" (Homily 1).
Gregory the Wonder Worker (c. 213-270) wrote: “Let us chant the melody that has been taught us by the inspired harp of David, and say, ‘Arise, O Lord, into thy rest; thou, and the ark of thy sanctuary.’ For the Holy Virgin is in truth an ark, wrought with gold both within and without, that has received the whole treasury of the sanctuary” (Homily on the Annunciation to the Holy Virgin Mary).
The oldest prayer to Mary (c. 250-280) says, "Beneath your compassion, We take refuge, O Mother of God: do not despise our petitions in time of trouble: but rescue us from dangers, only pure, only blessed one" (Sub Tuum Praesidium, John Rylands papyrus 470, held at the University of Manchester).
Dr. Lugwig Ott wrote: "The Latin Patristic authors unanimously teach the doctrine of the sinlessness of Mary. St. Augustine teaches that every personal sin must be excluded from the Blessed Virgin Mary for the sake of the honor of God (propter honorem Domini) [De natura et gratia, 36, 42], St. Ephrem the Syrian puts Mary, in her immaculateness, on the same plane as Christ. According to the teaching of St. Thomas the fullness of grace which Mary received in the active conception (according to modern theology, in the passive conception) implied confirmation in grace and therefore sinlessness (Summa III, q. 27, art. 5 res. 2).
Blessed Pope Pius IX declared in c. 1854 that Mary was free from all stain of sin: both original and personal (https://www.papalencyclicals.net/pius09/p9ineff.htm).
As we have seen, this Catholic doctrine did not come out of nowhere. It had a distinct train of thought, moving from Mary's purity, to her absolute purity. It was not totally and completely understood by people like St. Paul and St. Peter. Rather, as the very nature of development occurs, a greater understanding of the Divine Revelation - once for all delivered for the saints - continues to occur.