The follow has set my mind at ease, at least for now:
..no human words or works create the true presence of Christ’s body and blood in the Supper, whether it be the merit or the speaking of the minister or the eating and drinking or the faith of the communicants. Instead, all this should be ascribed solely to the almighty power of God and to the words, institution, and arrangement of our Lord Jesus Christ.
For the true and almighty words of Jesus Christ, which he spoke in the first institution of the Supper, were not only effective in the first Supper; they remain so. They retain their validity and power and are still effective, so that in all places in which the Supper is observed according to Christ’s institution and his words are used, the body and blood of Christ are truly present, distributed and received on the basis of the power and might of the very same words that Christ spoke in the first Supper. For wherever what Christ instituted is observed and his words are spoken over the bread and cup and wherever the consecrated bread and cup are distributed, Christ himself exercises his power through the spoken words, which are still his Word, by virtue of the power of the first institution. He wills that his Word be repeated, as Chrysostom says in his Sermon on the Passion, “Christ prepares this table himself and blesses it; for no human being makes the bread and wine, which are set before us, the body and blood of Christ. Rather Christ himself, who was crucified for us, does that. The words are spoken by the mouth of the priest, but when he says, ‘This is my body,’ the elements that have been presented in the Supper are consecrated by God’s power and grace through the Word. Just as the saying ‘be fruitful and multiply, and fill the earth’ [Gen. 1:28] was said only once and yet is continually effective in nature, causing it to grow and multiply, so these words were said once. But they are powerful and do their work in our day and until his return, so that in the Supper as celebrated in the church his true body and blood are present.” (Formula of Concord SD VII:74-76, Kolb/Wengert p. 606)
Here, too, if I were to say over all the bread there is, “This is the body of Christ,” nothing would happen, but when we follow his institution and command in the Supper and say, “This is my body,” then it is his body, not because of our speaking or our declarative word, but because of his command in which he has told us to speak and to do and has attached his own command and deed to our speaking. (Martin Luther [as quoted in the Formula of Concord], [Great] Confession concerning Christ’s Supper, quoted in FC SD VII:78, Kolb/Wengert p. 607)