Luther & the Lutheran tradition have insisted that "Holy
Communion is the true body and blood of our Lord Jesus Christ". All
communicants, whether "worthy" or not, receive this true body & blood of
Christ. Zwingli argued that the Lord's Supper is a memorial of Christ,
& that the body & blood of Christ cannot be present to communicants on
earth because, after the Ascension, Christ's body is in heaven, "at the
right hand of God".
Part of Luther's response was that the right hand of God means,
biblically, God's effective power, & that "the right hand of God is
everywhere". He argued that in the Incarnation the divine omnipresence
is communicated to the humanity of Christ so that he can be present
everywhere.
The later Reformed tradition - especially Calvin - had a more
"realistic" view of the Sacrament than did Calvin, but still insisted
that communion with Christ was a spiritual one through faith, that
unbelievers did not receive the true body & blood of Christ, & that the
divine natutre of the 2d Person of the Trinity was present "outside" the
humanity of Christ - the "Calvinistic extra".
Thomas Torrance - especially in _Space, Time, and Incarnation_ -
has argued the Reformed case in the context of modern science.
N.B. The above is a brief Lutheran analysis, which I hope is
fair to - though not in agreement with - Reformed views on the matter.
George Murphy