The Israelites were already called to love one another in the Old Testament  Leviticus 19:18 but thou shalt love thy neighbour as thyself: I am the LORD.

Yet it seems we are given the same commandment AGAIN in the New testament. But, what makes it new is that Jesus calls us to love one another as HE loves us."A new commandment I give to you, that you love one another, even as I have loved you, that you also love one another." This is a new commandment because it is a greater kind of love than the kind we could provide on our own under the law. It is a divine love we are called to love with. The love under the law that believers were called to is without the ultimate sacrifice Jesus provided.