On 16 April, 1522 Huldrych Zwingli’s sermon titled Von Erkiesen und Freiheit der Speisen was published in Zurich at the printing house of Froschauer. It was a greatly expanded version of the actual sermon preached shortly after the Lenten Fast was broken, with his approval. Unlike Barth’s Romans, this book really did fall on the playground of the theologians like a bomb.
Zwingli’s point was simple- the Church wasn’t authorized to heft upon souls requirements foreign to the requirements of the Bible. Its tradition wasn’t superior to Scripture; Scripture takes precedence over tradition.
In his own words-
[They] had not so strong a belief in God, that they trusted alone in him and hoped alone in him, listened alone to his ordinances and will, but foolishly turned again to the devices of men, who, as though they desired to improve what had been neglected by God, said to themselves: “This day, this month, this time, wilt thou abstain from this or that,” and make thus ordinances, persuading themselves that he sins who does not keep them.
This abstaining I do not wish to condemn, if it occurs freely, to put the flesh under control, and if no self-confidence or vainglory, but rather humility, results. See, that is branding and injuring one’s own conscience capriciously, and is turning toward true idolatry…In a word, if you will fast, do so; if you do not wish to eat meat, eat it not; but leave Christians a free choice in the matter…
But when the practice of liberty offends your neighbour, you should not offend or vex him without cause; for when he perceives it, he will be offended no more, unless he is angry purposely. … But you are to instruct him as a friend in the belief, how all things are proper and free for him to eat.