The Reformed account begins by refusing the question in the form both Rome and Wittenberg put it. Calvin agreed with Zwingli that the bread stays bread and that the body of Christ is in heaven. He agreed with Luther that the communicant truly receives the body and blood, and not merely a reminder of them. What he denied was that receiving requires the body to come down. In the supper, on his account, the Holy Spirit is the bond who joins things that distance separates, lifting the believer to where Christ is rather than enclosing Christ in an element. The liturgical shorthand is the ancient invitation to lift up your hearts, which he took as a plain statement of what the rite is doing.
Two consequences follow, and both mark the position off from its neighbours. The gift is real, so the supper is not a bare sign and not simply an aid to memory; it is an instrument through which the Spirit genuinely feeds. And the gift is received by faith, so a person eating the same bread without faith eats bread only. That second point separates the Reformed position from the Lutheran one as sharply as anything else, because the Lutheran confessions hold the opposite: the unworthy receive the body and blood as truly as the worthy, to their own judgement.
The teaching runs through the Reformed confessional texts. It is set out in the fourth book of the Institutes of 1559, in the questions on the supper in the Heidelberg Catechism of 1563, in the Second Helvetic Confession of 1566, and in the Westminster Confession of 1646, which states that the elements remain in substance what they were while worthy receivers really and indeed receive Christ crucified.