But in the moment of the Virgin’s conception the Holy Spirit purged and sanctified the sinful mass and wiped out the poison of the devil and death, which is sin.This reminded me of a similar line from the 1540 material that had been set forth as showing that Mary was immaculately conceived:
all that flesh and blood of Mary's has been purified in conception, so that nothing sinful remains.Notice that in the translation (one of many translations that has been made) there is some ambiguity about whose conception it is. In the first quotation I've provided, there's a similar ambiguity. In both cases, the ambiguity goes away as soon as one looks at the context. I've already shown the context for the 1540 quotation (here). And Mr. Swan has provided the context for the 1544 quotation (here), a portion of which I'll reproduce below:
The flesh of Christ comes forth from an incestuous union; likewise, the flesh of the Virgin, His mother, and of all the descendants of Judah, in such a way that the ineffable plan of God’s mercy may be pointed out, because He assumed the flesh or the human nature from flesh that was contaminated and horribly polluted.As you can see, context is key. "Mary's conception," or "the conception of Mary" (or replace "Mary" with "Virgin") can refer to two very different things: it can refer to the conception of Mary in the womb of her mother, and it can refer to the conception of Jesus (or any of his ἀδελφοὶ - look up its etymology). In the latter case, Mary is doing the conceiving, in the former case she is receiving the conceiving. The difference in meaning is significant and - in English - the difference can only be determined by looking at the context.
The scholastic doctors argue about whether Christ was born from sinful or clean flesh, or whether from the foundation of the world God preserved a pure bit of flesh from which Christ was to be born. I reply, therefore, that Christ was truly born from true and natural flesh and human blood which was corrupted by original sin in Adam, but in such a way that it could be healed. Thus we, who are encompassed by sinful flesh, believe and hope that on the day of our redemption the flesh will be purged of and separated from all infirmities, from death, and from disgrace; for sin and death are separable evils. Accordingly, when it came to the Virgin and that drop of virginal blood, what the angel said was fulfilled: “The Holy Spirit will come upon you and overshadow you” (Luke 1:35). To be sure, the Messiah was not born by the power of flesh and blood, as is stated in John ( cf. 1:13): “Not of blood nor of the will of a man, etc.” Nevertheless, He wanted to be born from the mass of the flesh and from that corrupted blood. But in the moment of the Virgin’s conception the Holy Spirit purged and sanctified the sinful mass and wiped out the poison of the devil and death, which is sin. Although death remained in that flesh on our account, the leaven of sin was nevertheless purged out, and it became the purest flesh, purified by the Holy Spirit and united with the divine nature in one Person. Therefore it is truly human nature no different from what it is in us. And Christ is the Son of Adam and of his seed and flesh, but, as has been stated, with the Holy Spirit overshadowing it, active in it, and purging it, in order that it might be fit for this most innocent conception and the pure and holy birth by which we were to be purged and freed from sin. [LW 7:12]
Moral of the story: check the context of your quotations. In these cases, quotations that might sound like support for the Roman Catholic error of the Immaculate Conception end up being rebuttals to it.