The word Maundy is derived from the Latin word for “command.” The “Maundy” in “Maundy Thursday” refers to the command Jesus gave to the disciples at the Last Supper, that they should love and serve one another.
“My command is this: Love one another as I have loved you. Greater love has no one than this, that he lay down his life for his friends.” John 15:12-13 NIV
This took place as He celebrated His last Passover with them, also called the Last Supper. The gospel of John chapters 13-16 is sometimes called “The Upper Room Discourse.” Describing the place where this event took place.
His discourse was giving His Apostles their final instructions before His departure to the cross the next day. Good Friday.
Facing the agony of the cross, His heart and thoughts were heavy for the disciples and what they were about to experience through this impending event. He was giving them final instruction to help prepare them.
The shadow of the cross was already descending on Him, and He was thinking of them, not Himself.
Maybe that’s why Maundy Thursday is sometimes called “Thursday of Mysteries.”