Maundy Thursday: What is the Sacrament?

The Israelites said "What is it?" when manna fell from heaven (that's what 'manna' means: what is it?): but we now know what they did not know. We know what that bread foretold, we know Christ, and we know what he said: This is my body. And we know what it is for, as he said: "The forgiveness of sins"; so we are sure that our sins are forgiven by this his body and blood which we receive in the Sacrament. And we also know what it produces in us: a new life of a Christian, following as Christ taught, washing one another's feet. This means treating one another as he treated us, with forgiveness and mercy.