Augustine’s Sacramental Sign & Seal, in Luther.
For Luther, “The Sacrament fit into the frame work of “promissio” and “fides” (the Word of promise and faith), into which all of Luther’s theological statements fit.” Again, for Luther, ” (1) The Word confirmed by a sign was the most important part of the sacrament. (2) The Word had to be connected with a sign. (3) The Word, like every word, required only faith. The same was true of the sacrament. The principal distinctions between Luther’s view and that of medieval theology were: (1) For Luther the Word was the gracious promise of God directed to the gathered community, whereas the “forma” was characterized more by its magical effect. In fact the words of institution in the Mass were whispered like a magic formula by the priest. (2) The sacrament was not dependent on the minister and his “intentio”, but solely on the promise of God and the faith of the recipient. With this Luther equated the sacrament with the Word; it was for him, as it was for Augustine, “verbum visible,” the visible Word.” (Walter von Loewenich)
Augustine’s “crede et manducati” (Believe, and you have received the sacrament). “The body and blood of Christ were signs that assured the validity of the promise the way a seal validates a will.” (Luther, WA 6) Indeed THIS was and is the Real-Presence for Luther, as Augustine!