It's not just a spiritual change, but also a physical change as well. Every particle of a consecrated host and every drop of the wine in the chalice contains the body, blood, soul and divinity of Christ in its entirety under the appearance of bread and wine. It's not just a symbolic "spiritual change" that occurs at the consecration, but also a change of the substance of the bread and wine that occurs at the consecration. After the consecration, it only appears to be bread and wine, but it no longer is.
A twisted light for sure, but the question was why they want a consecrated host rather than something from a non-Catholic communion service, not what is the true nature of a consecrated host.