We are all born with original sin which was caused by our original parents bringing sin and death into the world. We have inherited that sin nature from the original fall from grace.
As was prophesied in the Old Testament a virgin will bear a son called Immanuel (Isaiah 7:14). That Son is to become the Lamb of God and a replacement for the Paschal Lamb of Passover which is emblematic of Christ as the feast of the New Covenant. This prophecy is important in that it illustrates the necessity of the perfect sacrifice. Not one of a perfection of the flesh as the Paschal Lamb refers but the perfection of the soul which requires a divine nature as no human alone could fulfill the perfection required by the Father but only the God-man in Jesus. Being fully God, He could not dwell and be nurtured in a vessel containing sin nor could the Lamb of God inherit the original sin of our original parents. So, out of necessity and in preparation to the blessed mother’s obedience she was saved by Christ at her conception. The blessed mother was in such a state of grace before conceiving and nurturing the unborn Jesus that she is described as being “full of Grace”. Of course being full of God’s grace leaves no room for sin.
Now keep in mind that some may argue that Jesus does not qualify as a type of the Paschal Lamb because the Paschal Lamb was required to be without any physical blemish. Certainly the wounds of Jesus by His scourging left Him as anything but a physically unblemished sacrifice. It is significant to acknowledge that the Paschal Lamb of the Passover saved one from physical death while Jesus being emblematic saves one from the death of the soul into sin. Therefore, the Lamb of God had the perfection of the soul necessary to atone for sin which causes spiritual death.
Furthermore, while the obedience of the Israelites at Passover instituted a special kinship of the people as the family of God so too does the new kingdom instituted by Christ’s atoning sacrifice institute a new kinship or Covenant signified by the fact that we are to eat the Lamb in all its Body, Blood, Soul, and Divinity just as the Israelites had to eat the Lamb to be saved. Just like them it could not be a symbolic Lamb but its real flesh consumed; so too are we to partake of the reality of the feast provided by our Lord.
People may argue that it is not possible for Christ to save the blessed mother at her conception as the atoning sacrifice on the Cross has not yet occurred; this same argument by critics of the Eucharist argue similarly. But the fact is that God dwells outside of time where everything is in the eternal present without future or past. In the Scriptures according to St. Johns account of Jesus’ Colloquy at Capernaum in chapter 6 he said, “do this in remembrance of me” as translated into English but this is often a misunderstanding as to what Jesus was really saying because in English “remembrance means to recall a past event which is an approximation of the Greek meaning since there is no corresponding English equivalent. . However, the Koine Greek word used was “anamnesis” which has in its meaning an expectation of a miracle which transcends time and place. So what was truly being conveyed by Jesus’ words recorded by St. John is that the disciples truly ate the sacrificed flesh and drank the spilt Blood of our Lord just as we do today sharing in that one sacrifice presented by our Lord and shared by the entire Church in all its glorious manifestations. Therefore His atoning sacrifice provides for all humanity past, present and future.