Mamacita says: The semicolon is important here; it separates two distinctly complete sentences that have a connection to each other. The new commandment is that we love one another. The second sentence instructs us that we love one another as He has loved us.
In hot desert countries, barefoot or sandal-wearing people always had absolutely filthy feet. To wash feet like that was considered a humble, mundane, pretty nasty task. It also personifies sacrificial love and hospitality.