Doctrines about Mary are Biblical
It's unfortunate that beliefs about Mary have become a source of division among Christians. Many Christians honestly do not understand what Catholics believe about Mary and why. Some deliberately misrepresent Catholic belief, which only serves to further divide Christians. Furthermore, these doctrines are not doctrines of Catholicism alone. Orthdox and Protestant Christians also admit that some if not all of these doctrines are biblically based. The following information I've summarized and pilfered from Catholic and Christian: An Explanation of Commonly Misunderstood Catholic Beliefs by Alan Schreck
Beliefs about Mary are not the primary focus of the gospels. Catholics believe that there is a hierarchy or order of Christian truths. That is not to imply that one particular truth is less "truthful" than another. But some doctrines derive from others, are said to be implicit, or reasonably follow from others doctrines that are more explicit in the deposit of faith.
Yet, not all Christians truths are equally central to the basic Gospel message. For example, official Catholic teaching has never considered beliefs about Mary as being equal in importance to truths about God--the Father, Son, and Holy Spirit. Truths about Mary are all related to the basic gospel message, though they are not the primary focus of the gospels. This principle has its foundation in the Bible. For example, in all the New Testament letters attributed to Paul, Mary is mentioned only once, and not even by name (Gal 4:4). This certainly does not prove that Paul never spoke about Mary, but it does indicate that the basic gospel could be proclaimed without focusing on Mary.
However, many other New Testament writings do speak about Mary, and Catholics therefore believe that it is important to have a correct understanding of her role in God's plan of salvation. The principle of the hierarchy of truths points out two extremes that must be avoided in Christian teaching about Mary. On the one hand, Marian doctrines must not be presented as equal in importance to the fundamental Christian truths about the nature of God and redemption. Mary must never be exalted to the status of "goddess" deserving the worship and adoration due only to God. On the other hand, Mary's role in God's plan of salvation must not be ignored nor neglected.
The following discussion is summarized and pilfered from material written by Frank Chacon and Jim Burnam of San Juan Catholic Seminars:
(Beginning Apologetics 6: How to Explain & Defend Marian Doctrines)
Mary and Sacred Scripture Typology
The Old Testament prepared the way for the New Testament. Persons and events in the OT prefigured, foreshadowed, anticipated, and symbolized persons and event in the NT. The OT persons and events are called "types" of the NT persons and events they prefigure. A type is a prophetic foreshadowing of its NT counterpart. For example, in Rom 5:14, St. Paul specifically calls Adam a type of Christ. The NT teaches that in the OT persons and events, we are to see doctrines that are made more explicit in the gospel. Thus, to be faithful to the NT, we must appreciate the right typology found in the OT.
There are three major OT types of Mary: Eve, the Ark of the Covenant, and Queen Mother.
Mary as the Second Eve:
The devil, a fallen angel, brought words of death to Eve; the angel Gabriel brought words of life to Mary. Eve, our mother in the flesh, disobeyed God and cooperated greatly in Adam's sin, which caused the fall of the human race. Mary obeyed God and contributed greatly to Christ's redemptive mission of the human race, as his mother and disciple.
OT type in Genesis 3 ... NT counterpart (Luke 1)
Fallen angel elicits Eve's 'no' to God ... Archangel elicits Mary's 'yes' to God
Adam loses grace for all mankind ... Jesus restores grace for all mankind
Eve cooperates in Adam's sin ... Mary cooperates in Jesus' redemption
The early Church Fathers made the obvious connection: Christ is the new Adam (1 Cor 15:45), Mary is the new Eve. After Adam and Eve sinned, Gen 3:15 prophesies a woman and her son who will be at total enmity with the serpent (Satan) and his descendents. The woman's son will crush the serpent's head. Since the man who crushes the serpent's head is obviously Jesus, the woman must be Mary.
The earliest church Fathers, such as St. Justin and St. Irenaeus, were quick to realize this Biblical typology. Although the human race fell through Adam, Eve's role was crucial. Jesus redeemed the human race, but Mary's role was likewise crucial.
The OT describes women (other types of Mary) who crush Israel's enemies (types of Satan). In Judges 4:17-22, Jael drives a tent peg through the skull of Canaanite general Sisera. Judges 5:24 celebrates her: "Blessed among women be Jael." Judges 9:50-55 describes a woman who drops a millstone on the head of tyrannical King Abimelech, fracturing his skull. Judith delivers the Jewish people from the Assyrian army by beheading its commander-in-chief Holofernes with his own sword as he slept (Judith 12-13). Judith's heroism is celebrated with the words, "Blessed are you, daughter, by the Most High God, above all the women on earth; and bless be the Lord God ... who guided your blow at the head of the chief of our enemies" (Judith 13:18). The praise of Jael and Judith anticipate Elizabeth's' praise of Mary in Luke 1:42, "Blessed are you among women." Righteous men also crushed heads in the OT. David (a type of Jesus, who is the son of David) defeated the Philistine champion Goliath and chopped off his head with the giant's own sword (1 Sam 17:41-58).
In the OT, types of both Mary and Jesus (the woman and her seed) are shown crushing types of Satan. Jesus definitively crushed Satan's head on Calvary. Significantly, all four evangelists record that Calvary means "skull-place." Satan thought he had struck Jesus a lethal blow on the cross, but it proved to be a minor wound ("you will strike at his heel"). Satan suffered the mortal wound ("he will strike at your head") as Jesus destroyed our bondage to sin and death.
Who was at Christ's side on Calvary? Mary. What does Jesus call her? "Woman." (in Hebrew woman is 'Eve'). Mary is the New Eve. She is the "woman" of Genesis 3:15, the "woman" of John 2 whose intercession launched Christ's public and miraculous ministry, the "woman" of John 19 at the foot of the cross, and the "woman" of Rev 12 who, with her son Jesus, fights against Satan until the end. From Genesis to Revelation, the Bible describes Jesus and Mary together crushing the serpent's head.
Mary as the New Ark of the Covenant
The Ark was the holiest object in the OT religion. It was sacred because it carried the stone tablets of the Law that God gave Moses on Mount Sinai. In Ex 25, God gave meticulous instructions for constructing the Ark. It had to be made incorruptible from acacia wood, plated inside and outside with pure gold. It must be kept free from all impurity and profanation. In 2 Sam 6:6-7, God struck Uzzah dead because he dared to touch the Ark.
From the earliest centuries, Christians saw the OT Ark as a type of Mary. The connection is clear. That Ark carried the written Word of God; Mary carried the living Word. Mary is the living Ark of the living Word. The Ark helps us to see the biblical basis for doctrines like the Immaculate Conception and Assumption, which are not taught explicitly in Sacred Scripture, but which are taught implicitly through typology. Mary, like the OT Ark was made pure (Immaculate Conception), stayed pure (Perpetual Virginity), and kept from corruption (bodily Assumption into heaven).
It is also significant that in Rev, after seeing a vision of the OT Ark, John immediately sees a vision of a woman (Mary), thereby further connecting the OT Ark to the NT Ark--Mary. Far from an invention, the Feast of the Assumption dates back to the early centuries of Christianity. The liturgy of this feast is filled with OT readings which reference ... the OT Ark. This indicates that the early Church understood Mary to be the New Ark.
Moreover, God's chosen people in the OT used the Ark of the Covenant as a guide in their journey into the promised land (Num 10:33; Josh 3:3,6,11,14). Moses and his people also used the OT Ark of the Covenant in their battle against adversity (Josh 3:13-17) and against their enemies (Joshua 6). Likewise, you may find Catholics who place Mary (the new Ark) in a prominent place in their faith journey, turning to her frequently in their fight against evil. In the OT, the actions of Moses and God's people did not prove they worshipped the Ark. Any effects the Ark had in guiding them and battling adversity came only from God. The same is true for Catholics who turn to Mary for her intercession. This practice, while not central to the Gospel message, does not detract from our love of the Lord and is not despised by our Lord. According to Luke's Gospel, Mary's soul magnifies the Lord and all generations will call her blessed.
Mary as the NT Queen Mother
The OT kings clearly prefigured Jesus Christ, the NT King of kings (Rev 19:16). Jesus, in his humanity, descended from King David. Therefore, the kings of Judah, who were from David's line, especially prefigure Jesus' kingship. Luke 1:32 says, "the Lord God will give him [Jesus] the throne of David his father." Interestingly, the wife of the king of Judah was not the queen. The queen was the king's mother. She was known as the Queen Mother. She had great honor and authority in the kingdom (see 1 Kings 2:19-20). The Queen Mother had an official position; she had to be deposed in order to be removed (1 Kings 15:13).
The OT Queen Mother prefigures or foreshadows the NT Queen Mother. Jesus, the NT King of kings, does not have a wife. His mother would be the NT queen. This is exactly what Revelation 12 describes. Mary gives birth to a son who will "rule all nations" (the NT King of kings), and she is the mother of the followers of Jesus (Rev 12:17). She is queen--she is wearing a crown of twelve stars. Rev 12 depicts Mary as the NT Queen Mother. By studying the great honor and dignity queen mothers had in the OT, we can appreciate the profound role God has given Mary, Queen Mother of all Christians.
In Jn 19:27, Jesus said to his mother, "Woman, behold your son." Then he said to the disciple, "Behold your mother." Jesus only spoke seven times from the cross. Here, He is doing more than just making domestic arrangements. The Church has always understood that Jesus was revealing to all of us, represented by John, that Mary is our mother. Jesus' words indicate He is giving an important revelation. Recall the words of John the Baptist: "Behold the Lamb of God" (Jn 1:29). Just as John is indicating something profound about Jesus, so is Jesus about Mary.
Let me finish by reiterating that Biblical truths about Mary are secondary in the hierarchy of truths. We must avoid the extreme of teaching Marian doctrines as equal in importance to the fundamental Christian truths about the nature of God and redemption. Likewise, we must avoid the other extreme of ignoring or neglecting Mary's role in God's plan of salvation.
The Second Vatican Council urged the theologians and preachers of the Catholic Church to avoid these extremes:
This Synod earnestly exhorts theologians and preachers of the divine word that in treating of the unique dignity of the Mother of God, they carefully and equally avoid the falsity of exaggeration on the one hand, and the excess of narrowmindedness on the other.... Pursuing the study of the sacred scripture, the holy Fathers, the doctors and the liturgies of the chruch, and under the guidance of the church's teaching authority, let them rightly explain the offices [roles] and priviliges of the Blessed Virgin which are always related to Christ, the source of all truth, sanctity and piety. (Second Vatican Council, Dogmatic Constitution of the Church, no. 67)