As Christianity continued to develop, new perceptions were drawn from how St. Paul understand Christ as the New Adam who completes and perfects creation (1 Cor. 15). Some early teachers in the other hand, understood Mary as less than perfect, they were even arguing that she could be ambitious and doubtful, others argued for her sanctification or consecration to God even before, her birth.
Mary’s conception being promulgated as “immaculate” by Pope Pius IX in 1854 was due to the doctrinal development in the West which was supported by a pious fervor. The intention was to symbolize that she had been protected from all stain of sin (the Latin word for stain is macula) by a unique and singular act of God, which was based upon the redemptive merits of Christ’s future.
In the Catholic Church, the liturgical feast of Mary’s conception, celebrated on December 8th, became the celebration of her “immaculate conception”. Mary is also said to be sinless in the Orthodox Church as well, though they didn’t describe her conception as immaculate because of some doubts which concerns the Western ideas about original sin.
Anyways, the belief in Mary’s assumption into heaven probably, was evolved from the tendency in early Christianity to describe her life in ways similar to that of her son. The end of her life was celebrated at the fifth century in the various places in a feast of her dormition, or “falling asleep”.
In an interesting line with that of Jesus, Thomas the apostle doubted her assumption until he saw her empty tomb, from which she has been assumed into glory. The eastern Christians tend to think of her assumption as something that occurred after her passing, while Western Christians usually understand her passing and assumption as a whole reality.
The dogma of the Assumption was declared by Pope Pius XII in 1950 as a singular gift to Mary and as an anticipation of the general resurrection of believers. Moreover, it is best understood as a dogma of hope which was extended to all Christians who strive to be faithful to Christ and who embrace his resurrection as their own.
The last chapter of Lumen Gentium explains Mary as the most faithful disciple of Jesus. By extension, her destiny represents our own longing for life without end.