Thinking Christians understand that a key difference between Catholics and Protestants is the Eucharist, and more particularly the Catholic belief that the substance (but not the appearance) of the bread and wine are transformed into the Body and Blood of Christ during the liturgy by the priest.
Marc Barnes expounds on why this Real Presence forms the foundation for another key Catholic doctrine, the notion that we are to see Christ in each other and that in doing so, we come to see and respect the dignity and worth of that person:
Protestants puzzle over how Catholics can see the person of Christ in a piece of bread. But the greater mystery seems to be how Catholics see the person in the face of the Protestant. Both parties live in a world in which the gaze sees, not people, but tools, objects, social classes, races — a media world full of media types. The idea of seeing a particular person rather than this or that thing, really seeing her as an unrepeatable life, an unfathomable mystery and an infinite value — it’s about as shocking and difficult as seeing God in bread and wine.
I can think of no better education of the eyes than Eucharistic adoration. By stretching the eye to its utmost, demanding that it see in an appearance the real presence of God, we are taught to see the person in and through any appearance. If I see God in bread, how can I not see the person in the prostitute? If I see the God-man in the tabernacle, how can I not see the man in the doorway? If I see the person of Christ lifted up in the hands of the priest, how can I can I not see the person of the newborn as she is lifted to her mothers breast? The most difficult task of the eye is completed at church — it makes seeing-in-the-world like walking after a sprint.
There's more. And it's worthy. Go and see.