Uh, the bread and wine become Jesus' Body and Blood.
Jesus speaks of no 'becoming'.
He says that the bread and the wine 'are' His body and blood.
OK. At one time the bread and wine were simply bread and wine, perhaps when they were made. At a later time they become Jesus' Body and Blood. Their essence (substance/quiddity/"whatness"/ nature) has changed. "Transubstantiation" simply means a change in substance.
He says that the bread and the wine 'are' His body and blood.
The understanding of the Eucharist goes back to the beginning of the 2nd century (Inrenaeus) and throughout the early Church. The Orthodox Church refres to the "alteration" or "change" from bread in the Body and Blood by invocation of the Holy Ghost, treating it as a "Mystery" as all Sacraments are. The Catholic Church shared that teaching, but eventually went one step further and made it into a dogma in a process that spanned several hundred years (13th to 16th century).
Lutheran Church holds on to a teaching of consubstantiation, related but essentially different from the Orthodox alteration/change and Catholic transubstantiation, in that the bread and wine remain bread and wine in which Jesus' Body and Blood "enter" the profane substances and "co-exist" with them. The Anglican Church speaks of "Real Presence" but doesn't elaborate.
These Orthodox/Catholic concepts of the Original Church evolved from the logical and necessary conclusion that not all bread and wine are His Body and Blood, but only this bread and wine. Obviously, this refers to the bread and wine at Lord's Supper, which is celebrated in Holy Liturgy (Eucharist).
Obviously, neither the bread nor the wine was His Body or Blood until He said so -- at which point it was.
He also didn't say "This is bread and my Body..." but simply "This is my Body..." Obviously, the bread ceased to be bread, and the wine ceased to be wine.
They appear to us as bread and wine for obvious palatable reasons, and one can think of those characteristics as illusionary or, as Catholics call them physical "accidents," but the appearance and substance are not the same.
So, it is clear that neither the Eucharistic bread remains bread, nor Eucharistic wine wine, and it is also clear that not all bread and not all wine are His Body and Blood.
The message behind this is to think and not just read.