Maundy Thursday is the Thursday before Easter, believed to be the day when Jesus celebrated his final Passover with His disciples. Most notably, that Passover meal was when Jesus washed the feet of His disciples in an extraordinary display of humility. He then commanded them to do the same for each other.

Christ's "mandate" is commemorated on Maundy Thursday---"maundy" being a shortened form of mandatum (Latin), 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. 

"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).