Maundy Thursday

Now on the first day of Unleavened Bread the disciples came to Jesus, saying, "Where will you have us prepare for you to eat the Passover?" He said, "Go into the city to a certain man and say to him, 'The Teacher says, My time is at hand. I will keep the Passover at your house with my disciples.'" And the disciples did as Jesus had directed them, and they prepared the Passover. When it was evening, he reclined at table with the twelve. And as they were eating, he said, "Truly, I say to you, one of you will betray me." And they were very sorrowful and began to say to him one after another, "Is it I, Lord?" He answered, "He who has dipped his hand in the dish with me will betray me. The Son of Man goes as it is written of him, but woe to that man by whom the Son of Man is betrayed! It would have been better for that man if he had not been born." Judas, who would betray him, answered, "Is it I, Rabbi?" He said to him, "You have said so."
Matthew 26:17-25

Now as they were eating, Jesus took bread, and after blessing it broke it and gave it to the disciples, and said, "Take, eat; this is my body." And he took a cup, and when he had given thanks he gave it to them, saying, "Drink of it, all of you, for this is my blood of the covenant, which is poured out for many for the forgiveness of sins. I tell you I will not drink again of this fruit of the vine until that day when I drink it new with you in my Father's kingdom.”
Matthew 26:26-29

Christ's "mandate" is commemorated on Maundy Thursday; which means "command."  It was on the Thursday of Christ's final week before being crucified and resurrected that He said this commandment to His disciples. Jesus and his disciples had just shared what is known as the Last Supper and he washed their feet saying:

"A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another.”
John 13:34