Jaroslav Pelikan is one of the foremost scholars and authors who has written on the topics of early church history, development of tradition, and the history of Jesus. This book is actually a companion to his other book, "Jesus Through the Centuries", and attempts to understand why Mary has played such a prominent role in church theology, devotion, and tradition.
This question becomes even more perplexing when one realizes that Mary's role in the gospels is very limited, and she is only mentioned once by name outside of the gospels. Yet, this did not prove a hindrance to the early church fathers who went about scouring the pages of the Old Testament to find references to the mother of our Lord. The one technique that proved most useful to the fathers was reading the Old Testament allegorically instead of literally. By employing this method the fathers were able to find typologial similarities between Eve and Mary. Therefore, by the end of the 2nd century Irenaeus was able to develop the comparison between Eve and Mary, so that just as the apostle Paul saw Christ as a second Adam, Irenaeus viewed Mary as a second Eve. Pelikan argues that since Paul began the process of applying such an allegory from the Old Testament to Jesus that it was not a stretch for the fathers to make the connection between Mary and Eve.
The next step in the developing Mariological process was the application of the title, Theotokos, or the Mother of God. The need for such a title stemmed from the many Christological heresies that were appearing during this time. By calling Mary Theotokos the fathers were able to guarantee that Jesus' humanity was safeguarded, and also that his divinity was upheld. Nevertheless, Mary's new title as Theotokos only strengthened the growing devotion toward her. Pelikan shows that Athanasius, the great orthodox theologian, makes reference to a Marian celebration in his writings. In addition, in his writings against the Arians Athanasius argues against the position that Jesus was God's most perfect and best creation, but instead reserves that honor for Mary.
When Pelikan arrives at the period of medeval history, he shows how Marian devotion blossomed into a full blown phenomena. During this time Mary was showered with such titles as Mediatrix, Queen of Heaven, Mother of the faithful and many other such titles. In Bernard of Clairvaux, Mary had a great advocate who spoke very highly of the Mother of God. Yet when it came to one of the most pivotal doctrines of Catholic theology, that of the immaculate conception, Bernard and Aquinas denied that the doctrine was a reality. They believed that such a doctrine made Mary immune from needing a savior and made her wonderful qualities seem less special. It wasn't until Duns Scotus argued that the immaculate conception saved Mary more perfectly by preventing her fall rather than rescuing her from a fall, that the doctrine became common in the West.
Finally, Pelikan dives into the period of the Reformation and illustrates that although the Reformers eschewed much of Marian doctrine that developed in the middle ages, they did not in fact abandon everything. The Reformers maintained that Mary was indeed the Theotokos, defended her perpetual virginity, and some even held to her immaculate status. What the Reformers disagreed with were the practices of praying to Mary and the saints, and the view of Mary as a Mediatrix. The Reformers believed that the role of Mediator belonged to Jesus alone, and that all prayer addressed to Mary and the Saints was superfluous and useless.
In the last chapters of the book Pelikan examines the Marian dogmas that have been promulgated by the Catholic Church: the immaculate conception and the Assumption. Pelikan traces the developments of these doctrines all the way from the fathers of the early church to the present day theologians and church officials who have expressed these views. Lastly, Pelikan shows how the person of Mary is an important person to all Christians and that she is an example of faith that everyone should strive to emulate.