“A new commandment I give to you, that you love one another; as I have loved you, that you also love one another. By this all will know that you are My disciples, if you have love for one another.”
Why did Jesus call this a “new” commandment, when He had long before inspired Moses to write, “You shall love your neighbor as yourself” ( Leviticus 19:18 )? That is the old part, but Jesus adds in John 13, “as I have loved you.” That is the new, much more challenging part. Jesus Christ willingly gave His life for us! What greater depth of love can there be ( John 15:13 )?
So, though God gives those who follow Jesus Christ and the Bible many things that make us stand out from the world, here He lists the most important one as love.
Matthew Henry put it this way: “This was what their Master was famous for; and therefore, if you see any people more affectionate one to another than what is common, say, ‘Certainly these are the followers of Christ, they have been with Jesus.’”