"The Lord’s supper testifies to us, first, that we have complete forgiveness of all our sins through the one sacrifice of Jesus Christ, which He Himself accomplished on the cross once for all; "
There claim causes them a problem. They take the once for all to mean the event 2000 years ago. So does that mean they never had to repent? They never had to put their trust in Jesus in this life? No, they forget that they have requirements for this life. The Mass is Christ’s grace earned from his once for all sacrifice 2000 years ago, brought forward and applied to our lives. Their question implies universalism if they think that everything with regard to salvation was COMPLETELY finished 2000 years ago.
and, second, that through the Holy Spirit we are grafted into Christ, who with His true body is now in heaven at the right hand of the Father,"
Most certainly Christ is physically present in heaven. The Mass however is not said to bring about a physical prescence, but a sacramental prescence of his BBSD. Didn’t he say “I am with you always until the end of time”? So quite obviously there is a prescence here and now. The Church sees that prescence at a higher level than Protestants (while we include the spiritual level as well). Still not contradicting that Christ is physically present in heaven in body and one day in body standing as a man will return to this earth.
" and this is where He wants to be worshipped. But the mass teaches, first, that the living and the dead do not have forgiveness of sins through the suffering of Christ unless He is still offered for them daily by the priests; and, second, that Christ is bodily present in the form of bread and wine, and there is to be worshipped. Therefore the mass is basically nothing but a denial of the one sacrifice and suffering of Jesus Christ, and an accursed idolatry. "
Again they distort the view and then refute it. Don’t they worship Christ’s spirit in the here and now, present. Not just in heaven but on earth. Actually Christ’s offering is in heaven continuously and is not another sacrafice or a daily one, but rather the Mass opens a window in to the ongoing sacrifice in heaven. Scott Hahn’s Lamb’s Supper will give you a deeper grasp of this. We are participating in the sacrafice at Calvary in and unbloody manner. It is as if we are there. The Mass and Calvary cannot be separated and so he is in error.