I find the Marian dogmas (Assumption and Immaculate Conception) the most difficult to defend. Historic evidence is rather scant, and Biblical evidence is almost non-existent.
Opponents of the Immaculate Conception often point out that St. Thomas Aquinas (regarded as the greatest Doctor of the Church) did not support this doctrine. This is a case where the charge is simple (and accurate), but the defense is complex (the Galileo affair is another such situation, but the stakes are not as high because Dogma is not involved).
If the subject is Eucharist, I’m all in. But Marian doctrines are another thing.
Maybe this is because, as a protestant, I found the Marian doctrines the most difficult to accept. I only came to accept them because I came to accept the teaching authority of the Church, and once I did that, I was obliged to accept (at least with the intellect) everything the Church teaches.
You know, that’s really interesting. Because when I look at the Scriptures and the Church’s Tradition, I see tons of support for the Marian doctrines – including the Assumption, her perpetual virginity and Immaculate Conception, but especially Mother of God. I used to have difficulty finding the Immaculate Conception and Assumption in the Church Fathers, but that was before I started reading them on my own. If you rely on lists that pull quotes out, then it may seem like there isn’t strong support. But if you understand how doctrines are sometimes implied obscurely in the Fathers rather than stated directly, it becomes easier to see where their writings continuously pushed forward the doctrines of our Faith until they were officially proclaimed.
For example, with the Assumption, while the early Fathers don’t usually say simply, “Mary was taken into heaven,” many of them do talk about how she defeated death (Irenaeus, Tertullian, Justin Martyr), and at least one early Father (Hippolytus in 235 A.D.) made the important observation that Mary was imperishable (which literally means unable to die). The Scriptural testimony includes John’s testimony that Mary was bodily in heaven, but also many clear prophesies of the Assumption, such as the prophesy that the Messiah’s queen would be taken to His right hand – Psalms 45:9. Now if “Sit thou at my right hand, until I make your enemies your footstool” is a prophesy of Christ’s ascension, then surely “The queen stands at your right hand” is a prophesy of Mary’s assumption. For to place either Christ at the right hand of God, or the queen at the right hand of Christ, implies that they will be taken there.
Or take the prophesy contained in the Song of Solomon, that God would call out to His daughter, “Arise, my love, my fair one, and come away, O my dove. In the clefts of the rock, in the covert of the cliff, let me see your face.” Canticles 2:13-14. For the Scripture commands, and the woman arises. What woman, then, has risen into heaven except Mary? For no one else is even claimed to have done this but in our faith.
Then there’s the various hymns about the Ark of the Covenant going up with the Messiah to heaven. 2 Chronicles 6:41-42 is clearly messianic in this regard, and Psalm 132 picks up that refrain and makes it a prophesy of the Messiah. Now it would be well to ask those who do not accept the Assumption: how then did Christ fulfill this prophesy? Why is He foretold to arise with His ark, and what is the ark He is supposed to take with Him? Protestants have no answer for that question, but the fact that He would arise with His ark is contained in one of the most important Messianic psalms of the Old Testament.
With the Immaculate Conception the evidence is even more sublime. The Church Fathers not only talk constantly about Mary defeating the “original deception” of our first parents, (and that goes back to the second century and continues from then until today,) but some of them come right out and explicitly state that Mary was formed without original sin, such as Proclus of Constantinople in Homily 1. He lived in A.D. 446. Genesis 3:15 is a prophecy of the redemption. The woman is Mary, her seed is Jesus, the serpent is the devil, “he shall strike at your head” means the devil and sin will be defeated, and “you shall strike at his heel” means Christ’s foot will be wounded (think of the nail). The key is that it comes right after the Original Sin was committed. God is promising the removal of sin in the enmity with Satan (and his defeat) that is shared by Jesus and Mary. So Mary and Jesus had no sin because they were part of the redemption and removal of sin planned by God. It’s all in that prophesy.
Not to mention that Gen. 3:15 was spoken not only with reference to the serpent, but with reference to Eve herself, making it a promise of a new Eve. Now Mary would not make a very good new Eve if she had the very same fault for which the old one was replaced. So the very fact that Scripture promises a woman in place of Eve, as a response to the sin that Eve committed, implies that the new woman will not share the defect that Eve transmitted.
I could go on, but suffice it to say that to me the doctrines of the Assumption and Immaculate Conception and the other Marian doctrines are absolutely established in Scripture, not only by the New Testament but by the prophesies, and that gives me comfort when reasoning with Protestants about them.