On Maundy Thursday, Jesus gave his disciples a new command: to love one another as he has loved us. While the command to love had been given in the Old Testament law, Jesus deepens and redefines that law with his own example of love, first in washing the disciples' feet, then in dying on the cross for his people (which is what the foot-washing pointed to).
Further, Jesus says this love his disciples have for one another will show to the world that we belong to Jesus. Francis Schaeffer explains: "The command Jesus gave to His disciples during His last Passover is the universal mark of the Christian. Upon His authority, He gives the world the right to judge whether you and I are born again Christians on the basis of our observable love toward all Christians."
That is the challenge of Maundy Thursday: We must love one another as Jesus loved us. But there is also comfort: We do not have to conjure this love up inside ourselves, or produce it in our strength. The love with which we love others is the love of Jesus himself. Having given us his love, we can now give his love to others. Because he has shared his loved with us, we can share that same love with one another. Because he has poured his love into our hearts, we can pour his love into the the hearts of our fellow disciples.
How do we know if we have our fellow disciples as Jesus has loved us? Love is always defined by God's law. Later that night in the upper room, Jesus taught that we abide in his love as we keep his commandments (John 15:9-10). Love is not just a feeling. Love is a course of action dictated by God's law. As we treat one another lawfully, from the heart, we may know we are fulfilling the love command.
For further reading: