The Lord’s Supper occupied Zwingli from 1522 onwards with things coming to a head at Marburg in 1529. Between these two critical dates amidst disputing with the Papists and the Anabaptists, Zwingli had to explain to friends and foes his view.
On 1 March 1526 Zwingli published his Ad Theobaldi Billicani et Urbani Rheii epistolae responsio. Here Zwingli glosses a letter from Billican and writes a letter to him and Urban in order to describe more fully not only his views but to point out their errors.
It’s a pleasant read. Enjoy.