I found this article from Desiring God about Maundy Thursday to be helpful:
In the UK a few years back a group of church leaders used a Maundy Thursday church service to do something extraordinary. As people entered the church for the Thursday gathering of Holy Week, elders greeted them on their knees in the entryway. Every attendee was invited to sit, and there, in the entrance of the church, the elders removed shoes and socks and washed the reluctant feet of every stunned attendee.
Maundy Thursday is like that — it shocks.
The term maundy in Maundy Thursday comes to us from the Latin root mandatum, or commandment, from Jesus’s words in John 13:34:
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.
Jesus had just finished washing the disciples feet. But what Jesus instituted here points to a sacrificial love of eternal significance…
The article continues:
On Maundy Thursday the Creator of the universe bent down to his knees to wash the dirt from the callused feet of his followers. And as he scrubbed away the dirt, he scrubbed from his Bride all possible justifications for ethnic and economic hierarchies. He radically upset cultural norms. And now he calls us to go low in foot-washing-like service to one another.
But most importantly, Maundy Thursday reminds us the Son of Man willingly came to earth as a lowly slave, to serve us, to be crushed for us, to free us from the sin slavery that leads to eternal death. On his knees Jesus enacts for us a parable of the cross.
The disciples could not yet see the symbolic anticipation. The full explanation for why Jesus washed their feet would only become clear after the blood-bought atonement on Good Friday. Then the disciples would look back and understand the act of deep humility in the cross that brought us a once-for-all, head-to-toe, cleansing from all our sin.