The Dogma of Mary's Immaculate Conception

The dogma of the macroconception and Mary's perpetual virginity all follow from the original dogma of her divine motherhood. That was very early and vociferously defended by Saint Cyril against the writings of Nestorius. The idea of appropriateness or fittingness imagery from the Old Testament too, the sacredness with which sacred things should be treated. And so at the very least you can see that it seems very fitting for the vessel that carried the incurrent word to be immaculate.