If they really press for why, consider this:
- The Catholic Mass is in essence a perfect sacrifice in conjunction with the saints and angels of Heaven.
- Jesus is there as High Priest and sacrifice, as well as the host…
- The Communion is the NT “Passover”, instituted by God, worshiping God’s salvation plan for us by eating the body of the sacrificial lamb.
- All of this is the Catholic rite of Worship - a worship in OT is the a praise accompanied by a sacrifice.
Given all this, taking the Communion without believing this and the fundamental beliefs of Catholicism, is a waste of time, a grave sacrilege, and in reality an insult to those you are worshiping with. If they don’t believe Jesus is present at all in any of the three forms, it is sacrilege to consume “the wafer” (that would be like using Menorah candles for a non-religous purpose). If they do believe Jesus is there in 1 or more of the forms, it is an insult to Jesus because they do not believe all that the Mass and Catholicism is, as told to us by Jesus. They might get hurt then
Imagine a Catholic going in to sit down and have Passover dinner with a group of Orthodox Jews, and afterwards grabbing the Menorah candle for a little more light while reading the evening paper. I suspect the Jewish people would be pretty upset.