Yet while the origins of the cultus of Mary are rooted in popular devotion, it is supported by Scripture and Christian theology.
There are many titles of honour given to Mary, but in the litany,a long list of titles sometimes used in Catholic ceremonies as an invocation, she is called "ark of the covenant." and this title is fully scriptural. In the Old Testament the ark was the bearer of God's presence in Israel, but for some unknown reason it disappeared in Israel's wars and was never seen again. But at the incarnation Mary became the bearer of God's presence, carrying him in her womb, so symbolically she did the job of the ark and therefore the church rightly gives her this title.
This takes us to Mary's vital role in salvation history, the story of God's dealings with humankind. They believe that at the Annunciation [recounted in Luke chapter 1] she was visited by the archangel Gabriel to announce to her that she was to be the mother of the messiah, and her response was to willingly accept the tremendous and daunting challenge. Some Christians believe that without her willing acceptance of her role in God's plan the incarnation, God's becoming human in Jesus Christ, might not have happened. They believe that God was waiting on someone to say yes, and that someone was Mary. She is therefore a major player in salvation history, clearly subordinate to God, but an important human agent of God's will.
The Orthodox Church, which in many teachings is similar to the Catholic Church, rates Mary very highly and offers her significant devotion, awarding her the title of Theotokos, the bearer of God. This title is not formally used in the Catholic Church, but it is known, valued and respected by Catholics, who sometimes use it.
I was in Crete on August 15th one year, the feast of Mary's assumption into heaven and became aware of just how much the Orthodox celebrate the Theotokos. The traditions of the Palestinian church were that she was so holy that God took her straight to heaven, body and soul, when she died. As she is recorded as having died, it seems that the belief is that she was accorded the privilege of sharing in Christ's resurrection ahead of his other followers. The Christian teaching is that we will all resurrectas he did, but she was privileged to be resurrrected earlier than others.
The Reformation caused a decline in devotion to Mary, as the reformers smashed many of her shrines, including England's shrine at Walsingham in East Anglia, and I do not think that this has been good for the church, for it cut off a popular and emotionally satisfying aspect of Christian devotional living. Marian gardens were lost and there are few left. A few have been revived in England and some remain in monasteries in Europe. But the cult of Mary still retains its power to inspire devotion and her shrines, such as Lourdes and Fatima, are still popular.