St. Alphonsus de Liguori wrote about Mary’s Immaculate Concpetion in his classic work: “The Glories of Mary.” Here is the relevant section: DISCOURSE I. ON THE IMMACULATE CONCEPTION OF MARY.
Also, here are a few Bible verses and a short explanation of how they apply to Mary’s Immaculate Conception, which I compiled to be used for praying the rosary while meditating on Mary’s Immaculate Conception:
As a lily among the thorns, so is my love among the daughters. (Songs 2:2) is a reference to her being pure, unlike all other daughters of Eve.
Thou art all fair, O my love, and there is not a spot in thee. (Songs 4:7).
One is my dove, my perfect one is but one. (Songs 6:9]).
Behold, a little cloud arose out of the sea…. (1 Kngs 18:44a) the mist that rises from the sea has no salt in it and the salt represents original sin into which all are conceived except for Mary (and Jesus, of course).