The mystery at the center of the true Body and Blood
The Church teaches that the bread and wine truly become the Body and Blood of Christ through the Eucharistic prayer and the work of the Holy Spirit. This is why the Liturgy approaches the altar with awe, why the holy gifts are handled with care, and why the faithful prepare before receiving.
This is My body... This is My blood of the new covenant, which is shed for many for the remission of sins.
What “Truly Become” means
The Church does not reduce the Eucharist to a mental reminder. Christ’s command, “Do this in remembrance of Me,” is fulfilled inside worship, blessing, thanksgiving, and invocation of the Holy Spirit. The mystery is received by faith, not dissected as a chemical change.
My flesh is food indeed, and My blood is drink indeed.
Why this changes how people behave
If the Eucharist is truly the Body and Blood of Christ, then the reverence around Communion is not decoration. The silence, fasting, confession, careful distribution, and prayers after Communion all flow from the same belief: the faithful are receiving Christ, not a religious object.
How to ask about it
If you come from a church that uses different language, ask the priest how the Liturgy itself teaches this belief. The best answer is often found by listening to the prayers around the altar, especially the prayers of institution, the invocation of the Holy Spirit, and the Communion prayers.