As discussed in the article on Communion Reality Jesus made a very big deal about eating flesh and drinking His blood.
When Jesus told those following Him that they must eat His flesh and drink His blood many turn away and stopped following Him.
At the last supper Jesus again spoke of His Flesh And Blood, using the bread to represent His flesh and the wine to represent His blood.
Because the early Catholics understood how adamant Jesus was about us eating and dring His Flesh And Blood they overthough the communion and conceived of transsubstantiation.
Transubstantiation is a knock-off of abiding In Christ Jesus. It gives believers a false sense of arrival when the one and only destination for each of us is In Christ - in Spirit And Truth.