Catholic C: Why do we believe the Immaculate Conception of Our Lady? Catholic B: This is one of the four Marian dogmas. Our Catechism explains: "To become the mother of the Saviour, Mary “was enriched by God with gifts appropriate to such a role.”... in order for Mary to be able to give the free assent of her faith to the announcement of her vocation, it was necessary that she be wholly borne by God's grace." In 'The Glories of Mary', St Alphonsus explained in-depth how fitting it was to the Holy Trinity, let me share some points with you: ● Since the Eternal Father destined Mary for the restorer of the lost world, and mediatrix of peace between man and God, so she should not appear as a sinner and enemy of God, but as his friend, and pure from sin. ● God destined Mary to crush the head of the serpent, therefore she should not first be conquered by Lucifer, and made his slave; instead she should be free from every stain and from all subjection to the enemy, and remaining free from every stain of sin to the end, so she could conquer the devil. ● The Eternal Father also destined Mary for the mother of His only begotten Son, at least for His Son’s honour, the Father would create her pure from every stain and adorn her soul with every grace, that it might be a worthy habitation for a God. ● God can give the grace to Eve to come into the world immaculate; He can certainly bestow it on Mary. ● Since the Son could select a mother according to his pleasure, surely He would choose one befitting a God. Who would choose a slave for his mother instead a queen? Or an enemy of God instead a friend of God? Indeed, it is fitting that a most pure God should have a mother pure from all sin. ● If Our Lord gave us the command to honour our parents, then when he became man, should also observe it himself, which included created His mother immaculate when He was able to do so.  ● Who does not want a beautiful bride? If so, the Holy Spirit would surely use His power to make Mary - His spouse, as beautiful as He possibly can. Also because this divine spouse loved Mary from the beginning, more than all the saints and angels united, we can think of the swiftness of the Divine Spirit, in making her His spouse, before Lucifer can take possession of her. Yes, we believe this dogma. St Cyril of Alexandria says: Who has ever heard of an architect building a house for his own use and then giving the first possession of it to his greatest enemy?