The Immaculate Conception:

one of the topics I thought I knew in grade school, until my religion teacher proved me wrong. The Immaculate Conception is a teaching of the Church that Mary, the Mother of Jesus, was preserved from original sin from the moment of her conception  (not Jesus'). 

Catholic teaching purports that in order for Jesus to have been born without sin, he would have to have been conceived within a sinless human. If Mary had been born with the consequences of original sin, then Jesus would inherit this sin nature through her. Instead, God prepared for the incarnation of His Son by preparing Mary to bear Jesus Christ, through her Immaculate Conception.

Here is a neat comparison showing Mary as the Ark of the New Covenant from Catholic author and apologist Steve Ray. Not only is this creative and informative, but it also demonstrates the importance of familiarity with scripture and how this deepening of our faith can show us a deeper picture of the sacred liturgy, particularly as it relates to Christ, the Divine Lamb.

Mary the Ark as Revealed in Mary's Visit to Elizabeth

Golden Box: Ark of the Old Covenant	Mary: Ark of the New Covenant
The ark traveled to the house of Obed-edom in the hill country of Judea (2 Sam. 6:1-11).	Mary traveled to the house of Elizabeth and Zechariah in the hill country of Judea (Luke 1:39).
Dressed as a priest, David danced and leapt in front of the ark (2 Sam. 6:14).	John the Baptist — of priestly lineage — leapt in his mother's womb at the approach of Mary (Luke 1:41).
David asks, "How can the ark of the Lord come to me?" (2 Sam. 6:9).	Elizabeth asks, "Why is this granted me, that the mother of my Lord should come to me?" (Luke 1:43).
David shouts in the presence of the ark (2 Sam. 6:15).	Elizabeth "exclaimed with a loud cry" in the presence of the Mary (Luke 1:42).
The ark remained in the house of Obed-edom for three months (2 Sam. 6:11).	Mary remained in the house of Elizabeth for three months (Luke 1:56).
The house of Obed-edom was blessed by the presence of the ark (2 Sam. 6:11).	The word blessed is used three times; surely the house was blessed by God (Luke 1:39-45).
The ark returns to its home and ends up in Jerusalem, where God's presence and glory is revealed in the temple (2 Sam. 6:12; 1 Kgs. 8:9-11).	Mary returns home and eventually ends up in Jerusalem, where she presents God incarnate in the temple (Luke 1:56; 2:21-22).

Inside the Ark

Inside the Ark of the Old Covenant	Inside Mary, Ark of the New Covenant
The stone tablets of the law — the word of God inscribed on stone	The body of Jesus Christ — the word of God in the flesh
The urn filled with manna from the wilderness — the miraculous bread come down from heaven	The womb containing Jesus, the bread of life come down from heaven (John 6:41)
The rod of Aaron that budded to prove and defend the true high priest	The actual and eternal High Priest