Hello,
Why does the Catholic Church teach that the body and blood of Jesus is in both the bread and the wine instead of the body being the bread and the blood the wine?
It’s a theological doctrine called “concomitance.”
Bear with me here, because I have to start from the beginning.
When Christ died on the cross, He died from (technically and biologically) exsanguination literally a loss of blood. That means that, upon His death on the cross, the literal flesh of Christ and the literal blood of Christ were separated. A human body without blood cannot be alive, and neither can blood truly be alive outside the body.
Upon the resurrection, His body once again was alive—truly and completely. In order for His flesh to be alive, there would have to be blood in His system. Without the blood, He would not be genuinely resurrected. Not to be silly about it, but without blood in the resurrected body, He would be an animated (ie moving, speaking) body, but not actually human; since there’s no such thing as a living human body without blood flowing through it. If His flesh were alive without blood flowing through the system, then there was no true resurrection, only a trick or an illusion.
A living human being is always both flesh and blood together.
Since the Eucharist is Christ’s body; since it is His living and resurrected Body, that Body must necessarily be both flesh and blood together.
That gets us back to concomitance.
Since we say (and rightly believe) that under the Eucharistic species, both the Body of Christ and the Blood of Christ are truly the living Christ, that living Christ is “composed” (so to speak) of both His Flesh and His Blood together, regardless of whether we are speaking of the (species of the) bread or the (species of the) wine or both together, such as when they are mingled in the chalice, or by intinction.
If the consecrated host is “only” the flesh of Christ, to the exclusion of the blood, then it would not be the living flesh of Christ (because flesh without blood is not living)–it would instead be the dead flesh of Christ. Naturally, this is not the case. The same is said about the Blood.
In fact, when you think about it, we say that the consecrated Host is the “Body of Christ” (in Greek, soma) and not the “flesh of Christ” (in Greek Sarx) so we are already saying that the Host is “flesh and blood” because a living body is always “flesh-and-blood.”