This is actually somewhat of a myth. Because Luther preached on Marian feast days (but eventually rejecting some of those feast days), it’s assumed he had some sort of deep profound veneration of Mary, and all these Marian feast day sermons he preached are simply filled from start to finish about Mary.
This just isn’t so.
I’ve read a large number of these sermons, and I also have quite a good collection of these sermons. More often than not, the emphasis isn’t on Mary at all.
Sure, he mentions her, or may refer to a passage of Scripture in which she’s the topic, but one finds that Mary is usually not the main subject, Christ is. Here is one of those sermons on Luke 1:26-38. Note how Luther’s main concern is Christ, not Mary. Examples from Luther’s sermons similar to this could be multiplied.
This is not to suggest that there are not passages in which Luther says some nice things about Mary. These certainly exist, and I’ve compiled or worked through many of them, locating contexts, etc. But this does not equal a contemporary Roman Catholic understanding of Mary, at all. I blame a number of Roman Catholic apologists for finding more in Luther’s words than is actually there in context.
Regards, James Swan