On December 8, 1854, Pope Pius IX spoke directly from the Chair of St. Peter (also known in Latin as "Ex Cathedra" where the Pope makes an infallible declaration regarding the teachings of the church) declaring the Dogma of the Immaculate Conception of Mary.
Many people mistaken the Immaculate Conception as referring to Christ's conception, but in fact it is referred to his Mother Mary.
"The Immaculate Conception means that Mary, whose conception was brought about the normal way, was conceived without original sin or its stain—that’s what “immaculate” means: without stain. The essence of original sin consists in the deprivation of sanctifying grace, and its stain is a corrupt nature. Mary was preserved from these defects by God’s grace; from the first instant of her existence she was in the state of sanctifying grace and was free from the corrupt nature original sin brings." (Catholic Answers).
The Doctrine of the Immaculate Conception described Mary as not only perfectly sinless, but also receiving of supernatural holiness which was expressed in her life of virtue. She was perfectly impeccable through her constant awareness of God and her full reception of extraordinary graces. Due to the fact that she was born without the stain of original sin and free of all sin, but also free of concupiscence, she did not have the same disharmony of will, intellect and heart as we do. She lived a life of perfect morality and virtue, and we see her as the "model disciple."
Here are a few links for more facts on the significance of this Dogma: - https://www.catholic.com/tract/immaculate-conception-and-assumption - http://www.ncregister.com/blog/jimmy-akin/8-things-you-need-to-know-about-the-immaculate-conception - https://www.catholicnewsagency.com/resources/mary/popular-marian-devotions/the-immaculate-conception