Maundy Thursday marks the supper Jesus instituted with his disciples on the night before his death. This was intended to be a celebration of the Passover, which observed the rescue of God’s people from Egypt, who were saved from death by painting their doorposts with blood from an unblemished lamb. But at this meal, Jesus established a new covenant (in Latin, “mandatum novum,” which is where we get the term “maundy”). Jesus himself would now become the Passover lamb, giving his holy, unblemished body and blood for the sins of all people.
During this service, we also observe the custom of stripping the altar in solemn preparation for Good Friday.