What the Church says about Mary is primarily based on two facts. First, Jesus of Nazareth is God Almighty and perfect humanity in one person. Second, Mary is His mom. Thus, all of what we say about Mary is a confession about her Son.
The Scriptural proof for these two facts is well known and extensive; however we might just repeat Matthew 1:18, 22-23 here “Now the birth of Jesus Christ took place in this way. When his mother Mary had been betrothed to Joseph, before they came together she was found to be with child from the Holy Spirit. . . .All this took place to fulﬁll what the Lord had spoken by the prophet, ‘Behold, the virgin will conceive and bear a son, and they shall call his name Immanuel’ (which means, God with us).” Thus far the text.
Download a PDF of Apologia: Mariology.