Final answer:
The essential sign for the Eucharist is the consumption of bread and wine. It is a way for Christians to remember and participate in Christ's sacrifice.
Step-by-step explanation:
The action/essential sign for the Eucharist is the consumption of bread and wine. During the Last Supper, Jesus blessed the bread and said, 'Take, eat; this is my body.' He also blessed the wine and said, 'Drink from it all of you; for this is my blood of the covenant, which is poured out for the forgiveness of sins.' This act of consuming the bread and wine is seen as a way for Christians to remember and participate in Christ's sacrifice.