“The true preparation for this Sacrament consists of faith. There are two parts which you must believe. First, the bread and wine are the body and the blood of our Lord Jesus Christ….This faith is based on the words, “This is my body,” “This is my blood.” Do not fool with this faith! It has been the best thing about the papacy that this faith was preserved, that they did not doubt that the body and blood are present. Stick to the words!
“…But now in addition, a higher faith belongs to this and is more accurately called trust and is based on the words: “given for you,” and “shed for you for the forgiveness of sins.” These words are the promise….There is a promise, and in the promise a gift. Now where a promise is present and a gift is offered, trust belongs to this, that is: a heart believes that this will happen.
“…This is the true faith and the proper preparation for the Sacrament: that your heart clings to the Word of Christ….Now you have the true use of the Sacrament. It may be enjoyed in no other way than in faith, that both Christ’s body and blood and the forgiveness of sins are present. When you receive it, you should be certain: you have received the seal that God will forgive your sins.
“…A twofold faith is necessary. The first part believes that the words [of institution] are true. The second part believes that both are given for you, that you have the forgiveness of sins that brings righteousness and eternal life. The one faith says: This is Christ’s body. The other: This body is mine. Do not come forward without this faith! You must have this faith or at least ask for it.”
–Martin Luther, “Wednesday Morning, Holy Week, March 24, 1529,” The 1529 Holy Week and Easter Sermons of Dr Martin Luther, (St Louis, MO: Concordia Publishing House, 1999), pgs 63-69.