“But why (continues Luther,) is Sunday observed among Christians?  Although, all days are free and one day is like another, it is still necessary and good, yea, very necessary, that some one day be observed, whether it be Sabbath, Sunday or any other day.  For God designs to lead the world decently, and govern it peaceably; therefore he gave six days for work, but on the seventh day, servants, hirelings, and laborers of every kind, yea, even horses and oxen and other laboring animals shall have rest, as this precept requires, in order that they may be refreshed by rest.  And especially in order that those, who at other times have no leisure, may hear the preached word and thereby learn to know God.  And for this reason, namely, of love and necessity, Sunday has been retained, not on account of the Mosaic precept, but for the sake of our necessities in order that we might rest and learn the word of God.” [Note 2]

In his larger Catechism, Luther thus expresses himself. [Note 3]

“This commandment, therefore, with respect to its outward and literal sense, does not concern us Christians; for it is wholly an external thing, like other ordinances of the Old Testament, confined to certain conditions, and places, which are all now left free through Christ.  But in order that we may draw up for the uninformed, a Christian meaning of what God requires of us in this commandment, is is necessary to observe, that we keep the Sabbath-day, not for the sake of intelligent and learned (gelehrten) Christians; for these have no need of it: but in the first place, on account, of physical reasons and necessities, which nature teaches and requires for the common mass of people, men-servants and maid-servants, who attend during the whole week to their labor and employments, so that they may also have a day set apart for rest and refreshment (erquicken:) in the second, mostly for the purpose of enabling us to take time and opportunity on these Sabbath-days, (since we cannot otherwise attain them,) to attend to divine service, so that we may assemble ourselves to hear and treat of the Word of God, and then to praise him, to sing and pray to him.

“But this, I say, is not so confined to time, as ii was among the Jews, that it must be precisely on this or that day; for one day is not better in itself than another, but it should be daily attended to; but since the mass of the people cannot attend to it, we should reserve one day in the week, at least, for this purpose.  Inasmuch, however, as Sunday has been set apart from of old for this purpose, we should therefore let it remain so, that the Sabbath may be observed with uniformity, and that no one create disorder through unnecessary innovation.”

The above testimony of Luther is so distinct and decided, that he certainly would not have approved of the Augsburg Confession if Melancthon had introduced a different doctrine into it.  But there was no difference of opinion on this point, between these two luminaries of the church.