Full of grace DOES NOT EQUAL sinless.
Romans 6:14: “For sin will have no dominion over you, since you are not under law but under grace.” (cf. Rom 5:17,20-21, 2 Cor 1:12, 2 Timothy 1:9)
We are saved by grace, and grace alone:
Ephesians 2:8-10: “For by grace you have been saved through faith; and this is not your own doing, it is the gift of God – not because of works, lest any man should boast. For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them.” (cf. Acts 15:11, Rom 3:24, 11:5, Eph 2:5, Titus 2:11, 3:7, 1 Pet 1:10)
Thus, the biblical argument outlined above proceeds as follows:
1. Grace saves us.
2. Grace gives us the power to be holy and righteous and without sin.
Therefore, for a person to be full of grace is both to be saved and to be completely, exceptionally holy. It’s a “zero-sum game”: the more grace one has, the less sin. One might look at grace as water, and sin as the air in an empty glass (us). When you pour in the water (grace), the sin (air) is displaced. A full glass of water, therefore, contains no air (see also, similar zero-sum game concepts in 1 John 1:7, 9; 3:6, 9; 5:18). To be full of grace is to be devoid of sin. Thus we might re-apply the above two propositions:
1. To be full of the grace that saves is surely to be saved.
2. To be full of the grace that gives us the power to be holy, righteous, and without sin is to be fully without sin, by that same grace.
A deductive, biblical argument for the Immaculate Conception, with premises derived directly from Scripture, might look like this:
1. The Bible teaches that we are saved by God’s grace.
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.
The only way out of the logic would be to deny one of the two premises, and hold either that grace does not save or that grace is not that power which enables one to be sinless and holy. It is highly unlikely that any Evangelical Protestant would take such a position, so the argument is a very strong one, because it proceeds upon their own premises.
In this fashion, the essence of the Immaculate Conception (i.e., the sinlessness of Mary) is proven from biblical principles and doctrines accepted by every orthodox Protestant. Certainly all mainstream Christians agree that grace is required both for salvation and to overcome sin. So in a sense
my argument is only one of degree, deduced (almost by common sense, I would say) from notions that all Christians hold in common.
But you don't care, you just deny the premise held by every Evangelical Protestant, with unbiblical conclusions:
Full of grace DOES NOT EQUAL sinless.
None of the early reformers believed that Mary was a sinner which proves that modern day Protestantism is theologically chaotic. If Mary was a sinner, then Jesus would have had to repose in a sinful womb and been nourished with the blood of a sinner until His actual birth.
The notion that Mary was a sinner came out in the late 18th century. Before that, every Protestant denomination accepted her sinless nature.
Your flat out denial of what your own reformers taught is laden with lame excuses. It is the very nature of Protestantism to disagree with the reformers and their own scholars and reference manuals. You are preaching a man made 250 year old tradition and not aware of it.