Benedict XVI answered this question today in Turin where he celebrated Mass this morning during a one-day trip to the city.
"What is new is precisely this 'loving as Jesus loved,'" he explained. "The Old Testament did not give any model of love but only formulated the precept to love. Jesus, however, gave himself to us as model and source of love. This is a love without limits, universal, able to transform all the negative circumstances and all the obstacles into occasions for progress in love. [...]
"Giving us the new commandment, Jesus asks us to live his own love, which is the truly credible, eloquent and efficacious sign that announces to the world the Kingdom of God."
Image Source: AP Photos. Pope Benedict XVI, white figure at center on stage, prays in front of the Holy Shroud in Turin's cathedral, Italy, Sunday, May 2, 2010. Benedict XVI prayed before the Shroud of Turin, believed to be Christ's burial cloth.