1. The Bible teaches that we are saved by God's grace.Number 1 is true.
2. To be "full of" God's grace, then, is to be saved.
3. Therefore, Mary is saved (Luke 1:28).
4. The Bible teaches that we need God's grace to live a holy life, free from sin.
5. To be "full of" God's grace is thus to be so holy that one is sinless.
6. Therefore, Mary is holy and sinless.
7. The essence of the Immaculate Conception is sinlessness.
8. Therefore, the Immaculate Conception, in its essence, can be directly deduced from Scripture.
Number 2 and 3 are true but I think it misses the point. The angel isn't coming to Mary to comfort her because she is doubtful about her salvation. The angel is coming to Mary to tell her of her unique role. She is the "graced one" whom God has chosen to be the mother of God. God has graced her. God has shown a favorable disposition towards her and given her this role.
Number 4 is true.
Numbers 5 and 6 misread both the Vulgate and the Greek. Armstrong has a false understanding of what "full of grace" means. The Greek literally addresses Mary as the "Graced one." She is the one upon whom God has bestowed grace. Grace is not a substance but God's favorable disposition towards Mary. There are plenty of instances throughout Greek literature where someone bestows grace upon someone else and it doesn't have anything to do with injecting grace into the person. I'm not saying the term "full of grace" is wrong as it appears in the Vulgate. I'm not convinced that Jerome intended "full of grace" to be understood this way. And it does not follow that just because God looked favorably upon Mary in this very unique way that Mary is sinless. Grace is often shown in Scripture to sinful people. We are saved by grace apart from our works. God bestowing grace upon a person does not mean that the person has not sinned.
Numbers 7 and 8 try to divert our attention away from the real issues and assume a number of erroneous things about the Greek. Even if you were to wrongly conclude that Mary being full of grace meant that she was without sin, the text does not say she was always full of grace. Also, the sinlessness of Mary is not exactly the same thing as the doctrine of the immaculate conception. The Eastern Orthodox popularly teach that Mary was sinless as far as her actively sinning goes but deny the immaculate conception and say that Mary was born under the law of original sin (even though this is also denied by some Eastern Orthodox theologians). The Eastern Orthodox say that to teach that Mary was free from original sin would mean that Christ is not her redeemer and Mary very clearly confesses that Christ is her redeemer. Interestingly enough, Thomas Aquinas makes the same argument against the immaculate conception as do a number of significant medieval Western theologians. Eastern Orthodox theologians have also taught that the immaculate conception places Mary outside of the human race.
Among the pre-Nicean church fathers there was strong consensus that Mary was neither sinless nor immaculately conceived. They unanimously declare that Jesus is the only sinless one and both Chrysostom and Tertullian draw attention to examples of Mary's sin. The historic liturgy in use in the Eastern Church also declares Jesus to be the only sinless one. Post-Nicea there is a shift towards teaching that Mary is sinless among the church fathers but it's not until the middle ages that the immaculate conception and there was quite a bit of dispute in the middle ages over it.
The Roman church admits that there are no explicit statements in the early church fathers regarding the immaculate conception but that the teaching is implicit in the church fathers and that the church must continually grow and develop in her doctrine. But this is absurd because the early church fathers were not merely silent on the matter but pointed to actual times when Mary sinned and explicitly declared Jesus to be the only sinless. How can someone claim to be adhering to Apostolic tradition when they teach the opposite of what the church fathers taught? On a great number of issues there are times where the truth is held by a minority but if it is completely absent where is the tradition? How is it handed down if nobody is handing it down and everyone is explicitly denying it? How can it be implied when there is explicit denial? Perhaps we can extract an implicit denial of the Immaculate Conception from the Roman church's explicit teaching of the immaculate conception. It's perfectly reasonable that over time certain doctrines will be more clearly articulated over time but when a church body claims to be teaching something based on Apostolic Tradition that is the exact opposite of what everyone in the early was saying there is no basis for such a claim.
Armstrong has a series of articles examining Chemnitz's Examination of the Council of Trent. The bulk of the articles deal with the issue of Sola Scriptura and in a strange way Armstrong tries to shoehorn Chemnitz into an evangelical mold. Armstrong sets the stage as if the only two options are the two-source theory of Trent or me and my Bible in a closet. But Lutherans and the early church fathers held to the view that tradition serves an important role but is not another authoritative source for doctrine. Rather, Scripture provides the proper interpretive grid for understanding the Scriptures. The Apostolic tradition is cut from the same cloth as the Scriptures. The two source theory did not appear until about the 4th Century and did not become popular until the middle ages. The two source theory was officially adopted at the Council of Trent by the Roman church but there were a variety of different theories that existed up until that point. It can even be argued that with the dogma of papal infallibility that came later, Rome has deviated from the two source theory and instead now holds that the pope is the ultimate source of authority.
Armstrong also discusses the issue of Apostolic Succession. It is certainly true that you find some very strong statements in the early church fathers about the importance of Apostolic Succession. Some branches of the Lutheran church still have Apostolic Succession and it's a good physical representation of what is happening doctrinally. But what happens when physical Apostolic Succession (which itself is at times throughout history doubtful) results in bishops that do not uphold the Apostolic doctrines? Do you place your confidence in the physical line of succession or in the doctrines that were intended to be passed down? What about the modalist popes or popes that held to other heresies? The church seems to have placed a high value on Apostolic Succession but a much higher value on the Apostolic Doctrine. Both Cyprian and Augustine denied papal primacy.
In one article, Armstrong writes:
The central question is whether Chemnitz can prove that the Fathers (and, remember, not just a few scattershot examples, but en masse) believed in Lutheran distinctives, such as those I listed above:
1) imputed justification
2) faith alone (sola fide)
3) assurance of one-time justification and salvation
4) formal separation of justification and sanctification
Numbers 3 and 4 apply to Calvinism and evangelicalism but they are not true of Lutheranism. Numbers 1 and 2 do apply to Lutheranism but notice the standard that Armstrong sets up. If the standard for any doctrine is that the Fathers en masse approve of the doctrine, then a long list of doctrines that the Roman church now teaches would not pass muster. Many of the current doctrines of Rome are out rightly denied en masse by the church fathers. Imputed justification and sola fide may have gone through periods where they were found only among a minority of church fathers but they were never completely absent. Keep in mind that there was a period of time in which Arianism was also the position that was held en masse by the church.
Then Armstrong writes:
Moreover, as in the Bible and Tradition issue, the Protestant apologist has the burden of considering the overall theology of any given Church Father. Not only do Chemnitz and others who attempt the same thing, fail to show that the Fathers hold to the four Lutheran distinctives above, and other related ones, but they quickly pass over or completely ignore other relevant beliefs that would indicate an express disagreement with Lutheran (or "mainstream" Protestant) soteriology. I can think of a dozen such tenets, right off the bat (let's refer to them as "the dirty dozen"):
1) Infused, internal justification (as opposed to extrinsic, or external, or imputed)
2) Baptismal regeneration
3) Free will
4) The possibility of falling away from salvation (as opposed to "perseverance" or "eternal security")
6) The sacrifice of the Mass
9) Prayers for the dead (presupposes purgatory)
10) Salvation as a process, not a one-time proclamation or declaration
11) Faith and works organically, formally united (as opposed to being formally separated)
12) Sanctification and justification organically, formally united (as opposed to being formally separated)
[Lutherans fully accept #2, and pretty much #3 and #4, though in a somewhat different sense than Catholics do, but disagree with the other nine. They agree that works are compulsory in the Christian life, yet separate them from justification per se, which is solely imputed]This section is very strange because it begins by acting as if Chemnitz has to prove the church fathers denied all the things taught on this list in order to prove his case but then acknowledges at the end that Lutherans do not deny some of the things taught on the list. Armstrong acknowledges that Lutherans do not deny 2, 3, or 4 but there are also other things on this list which Lutherans do not deny.
In response to 6, Lutherans acknowledge in the Book of Concord that mass is a sacrifice. It is referred to as a euchastic sacrifice. What Lutherans deny is that it is a propitiatory sacrifice and Lutherans place the emphasis on the mass being Christ's body and blood rather than on the sacrificial aspect since Jesus said that this is his body and blood which is shed for you for the forgiveness of sins.
In response to 9, the Lutheran confessions do not condemn prayers for the dead. In fact, the Lutheran liturgical form for funerals includes a prayer for the departed. Prayers for the dead do not presuppose purgatory. The Eastern church has prayers for the dead but no doctrine of purgatory.
In response to 10, Lutherans do not teach that salvation is just some one time event that a person experiences at the time he first believes. We are in need of daily justification because we sin daily..
In response to 11, Lutherans do not separate faith from good works.
In response to 12, Lutheran do not separate justification from sanctification.
So in reality, we are left with 1, 3, 5, 7, and 8.
As for 1, Armstrong acknowledges that Chemnitz provides patristic support but basically says that he can provide more for the Roman Catholic view. But just because a view is more popular during certain periods of time that does not guarantee adherence to Apostolic tradition Arius' view of Christ was at one time the more popular view. You can read Chemnitz's quoations from the church fathers here: http://www.angelfire.com/ny4/djw/lutherantheology.chemnitzjustification.html
3 is very vague. What does he mean by free will? It's actually pretty easy to find a wide variety of views on the issue of free will among the church fathers.
5 is vague as well. The church fathers had a wide range of views on the issue of merit.
7 is very vague. Luther did write about penance and it is spoken about in different ways by different church fathers. You can read about the development of penance here: http://steadfastlutherans.org/?p=24314
8 is just kind of strange because the Eastern churches have no doctrine of purgatory and the doctrine remains ambiguous in the Roman church. Some speak of it as a place while other speak of it as a process. Some even refer to it as a purifying that happens instantaneously at death. The next pope will no doubt say something about purgatory that's a bit different than the current one and we're all supposed to declare whatever the current pope says to be Apostolic tradition.