Christ was the word that spake it.
He took the bread and break it;
And what his words did make it
That I believe and take it.
Those words of Elizabeth I are not half bad. The focus of Lutheran teaching with respect to the Sacrament of the Altar and when we can be assured that Christ is present in His body and blood with the bread and wine is an issue of the efficacy of the Word. Does the Word do what it says, deliver what it promises, and make that of which it speaks? Either yes or no...
Sometimes there are those who make this a transubstantiation issue but it is not. Transubstantiation has nothing to do with the sacramental moment but everything to do with trying to explain the what of Christ's presence. It insists upon a change (to the essence or substance, hence the name, while allowing the appearance or accidence to remain the same) which goes beyond Scripture. It is needless and fruitless as far as explanations go. It does little to assure and is, at best, a muddying of the waters. It pits what the eye sees against what the mind understands and in the end attempts to uncloak the mystery of the presence that can never be comprehended or explained but only believed and received.
The point here is the efficacy of the Word of God. Can we believe that it does what it says? It was a later generation of Lutheran dogmaticians that began to waver -- again in an attempt to distinguish Lutheran teaching from Rome. This was a foolish and dead end road that created more problems than it solved and posited the impetus for Christ's presence away from the Word of Christ to the mouth/faith of the receiver.
Much in the same way, Lutherans have been long accused of consubstantiation which holds that during the sacrament, the fundamental "substance" of the body and blood of Christ are present alongside the substance of the bread and wine, which remain present. Advocated by the medieval scholastic theologian Duns Scotus, consubstantiation has been erroneously identified as the eucharistic doctrine of Martin Luther. Luther refused a philosophical construct to define Christ's presence and simply called it the sacramental union.
The connection for Lutherans is incarnational theology -- just as the union of the human and divine became the one person by the word, so that in Mary's womb the Son of God became human flesh by the power of the Spirit, so by the Word, a sacramental union is created in which the flesh and blood of Christ are united with the bread and wine of the Eucharist in such way that the bread and wine are not lost or overcome nor the body and blood of Christ in any diminished. Lutherans understand the epiclesis to be implied in the agency of the Word and do not require a separate epiclesis apart from the way the Spirit works through the Word. Lutherans leave the mystery intact and let the Word be the focus and assurance that what is distributed by the hand of the priest (Pastor, if you prefer more modern parlance) and given to the communicant is nothing less than what that Word has promised -- hidden in bread the body of Christ and hidden in wine His blood just as in the incarnation hidden in human flesh is the fullness of the divine nature in the one flesh and blood person Jesus Christ.
This Word of Christ in the Words of Institution is no magical formula to effect the presence of Christ as some incantation to which Christ is obligated to submit but the Word He has given to His Church so that what He has given may be received. This Word is not captive to man so that any sort of unbeliever may speak it over bread and wine and confect the presence of Christ nor would children "playing church" inadvertently call down Christ's sacramental presence and it can also be said that when those who speak it have no intention of Christ's sacrament, there is no sacrament even though the Word be there and the elements be there (such as the Zwinglians who do not believe or intend the meal to be sacramental but merely symbolic).
So what supports this? I Corinthians 10:16: "The cup of blessing which we bless, is it not a communion of the blood of Christ? The bread which we break, is not a communion of the body of Christ?" AND Augsburg Confession, Article X: "1] Of the Supper of the Lord they teach that the Body and Blood of Christ are truly present, and are distributed 2] to those who eat the Supper of the Lord; and they reject those that teach otherwise." AND Apology Article X "55] And we have ascertained that not only the Roman Church affirms the bodily presence of Christ, but the Greek Church also both now believes, and formerly believed, the same. For the canon of the Mass among them testifies to this, in which the priest clearly prays that the bread may be changed and become the very body of Christ. And Vulgarius, who seems to us to be not a silly writer, says distinctly that bread is not a mere figure, but 56] is truly changed into flesh." [NB the word "changed" there] AND the second Martin, one of the authors of the Formula of Concord adds: "Therefore it is not a man, the minister, who by his consecration and blessing makes bread and wine into the body and blood of Christ, but Christ Himself, by means of His Word, is present in this action, and by means of the Word of His institution, which is spoken through the mouth of the minister, He brings it about that the bread is His body and the cup His blood.. .." Martin Chemnitz, Examen (English translation,Part II, CPH). Too long to be posted here, but look up Formula of Concord, Solid Declaration, VII.73-90.
This is what the Confessions speak to and how I was taught Eucharistic theology... While I know of other that claims to be Lutheran, this is what is true to the binding word of our Confessions...