From the Treasury of Daily Prayer:

Maundy Thursday, the Day of Commandment (Dies Mandati), most properly refers to the example of service given us by our Lord and the directive to love as we have been loved (John 13:34). Yet we must not forget the command given in the Words of Our Lord to “do this in remembrance of Me.” This day, with its commemoration of the institution of the Lord’s Supper, is set off from the rest of Holy Week as a day of festive joy.