Q: Why is it that some Catholics do not believe in Christ’s real presence in the Eucharist?
A: As a priest who has celebrated Mass for 40 years, as one who has distributed Communion for even longer, I’m not sure that the disbelief you describe is widespread.
Yes, it would be good if more Catholics responded “Amen” when the distributor announces “The Body of Christ” or “The Blood of Christ”— as the liturgy directs. Yes, almost all of us could show more reverence when we receive Communion.
Even so, most Catholics believe that Jesus is uniquely present in the Eucharist. They may not be able to explain that presence as well as St. Thomas Aquinas did. We know by faith that Jesus’ words of consecration change the reality of ordinary bread and wine into the reality of his Body and Blood.
The Church believed in the Real Presence for almost 1,200 years before it approved the term “transubstantiation” to describe what happens in the Eucharist. Our faith is in Christ, not in human words about Christ and his sacraments. Our words can nurture faith but can never substitute for it.