Probably the most astonishing Marian belief of Luther is his acceptance of Mary's Immaculate Conception, which wasn't even definitively proclaimed as dogma by the Catholic Church until 1854. Concerning this question there is some dispute, over the technical aspects of medieval theories of conception and the soul, and whether or not Luther later changed his mind. Even some eminent Lutheran scholars, however, such as Arthur Carl Piepkorn (1907-73) of Concordia Seminary in St. Louis, maintain his unswerving acceptance of the doctrine. Luther's words follow:
It is a sweet and pious belief that the infusion of Mary's soul was effected without original sin; so that in the very infusion of her soul she was also purified from original sin and adorned with God's gifts, receiving a pure soul infused by God; thus from the first moment she began to live she was free from all sin.
(Sermon: "On the Day of the Conception of the Mother of God," December [?] 1527; from Hartmann Grisar, S.J., Luther, authorised translation from the German by E.M. Lamond; edited by Luigi Cappadelta, London: Kegan Paul, Trench, Trubner, first edition, 1915, Vol. IV [of 6], p. 238; taken from the German Werke, Erlangen, 1826-1868, edited by J.G. Plochmann and J.A. Irmischer, 2nd ed. edited by L. Enders, Frankfurt, 1862 ff., 67 volumes; citation from 152, p. 58)
She is full of grace, proclaimed to be entirely without sin- something exceedingly great. For God's grace fills her with everything good and makes her devoid of all evil.
(Personal {"Little"} Prayer Book, 1522)
ルターは「無原罪の御宿り」を信じていたということですね。
下の部分はルターの著作からの引用になっていて、そこで
"thus from the first moment she began to live she was free from all sin."
「それゆえ誕生の最初の瞬間から、彼女（マリア）はすべての罪から解放されていた」
とルター自身がはっきり書いてます。
ただ、ルターはこの信条を全信者が信じるべき公式教義とすることには反対してました。つまり私的信条としてのみ認めていたわけです。
その点でルターの立場は、「無原罪の御宿り」を公式教義とした1854年以降のカトリックとは違いますが、当時においてはマリア崇敬の考え方についてそんなにローマ教会と違った見解ではなかったといえるんじゃないでしょうか。
