“A new command” is not really a new command (Lev 19:18) in one sense, but in another it is. He is not speaking here of love for all men, but for those within the brotherhood; the new thing here is the love that Christians have for each other because of their great love for Christ (1 John 2:7-10). The command to love is not new, but the motive to do so is. A comparison between 1 Cor 13 and the specific instructions to love in the Penteteuch will illustrate the difference.  Note the present tense  “keep on loving.”  The measure of our love for another is set by Christ’s love for us.

Leviticus 19:18  “‘Do not seek revenge or bear a grudge against one of your people, but love your neighbour as yourself. I am the LORD.

1 John 2:7-10  Dear friends, I am not writing you a new command but an old one, which you have had since the beginning. This old command is the message you have heard.  Yet I am writing you a new command; its truth is seen in him and you, because the darkness is passing and the true light is already shining.  Anyone who claims to be in the light but hates his brother is still in the darkness.  Whoever loves his brother lives in the light, and there is nothing in him to make him stumble.

1 Corinthians 13:1-13  If I speak in the tongues of men and of angels, but have not love, I am only a resounding gong or a clanging cymbal. If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but have not love, I am nothing.  If I give all I possess to the poor and surrender my body to the flames, but have not love, I gain nothing.  Love is patient, love is kind. It does not envy, it does not boast, it is not proud.   It is not rude, it is not self-seeking, it is not easily angered, it keeps no record of wrongs.   Love does not delight in evil but rejoices with the truth.   It always protects, always trusts, always hopes, always perseveres.  Love never fails. But where there are prophecies, they will cease; where there are tongues, they will be stilled; where there is knowledge, it will pass away.  For we know in part and we prophesy in part,   but when perfection comes, the imperfect disappears.  When I was a child, I talked like a child, I thought like a child, I reasoned like a child. When I became a man, I put childish ways behind me.   Now we see but a poor reflection as in a mirror; then we shall see face to face. Now I know in part; then I shall know fully, even as I am fully known.   And now these three remain: faith, hope and love. But the greatest of these is love.