Why do Christians love one another?

At the Last Supper, Jesus was troubled in His spirit as He contemplated what lie before Him - knowing who would betray Him.

John 13:22-25 (HCSB) The disciples started looking at one another—uncertain which one He was speaking about. One of His disciples, the one Jesus loved, was reclining close beside Jesus. Simon Peter motioned to him to find out who it was He was talking about. So he leaned back against Jesus and asked Him, “Lord, who is it?”

Jesus told them it would be the one to whom He gave bread, which was Judas. Jesus told him to do quickly what had to be done.

John 13:28-29 (HCSB) None of those reclining at the table knew why He told him this. Since Judas kept the money-bag, some thought that Jesus was telling him, “Buy what we need for the festival,” or that he should give something to the poor.

Then we read this glorious passage:

John 13:31-35 (HCSB) When he had gone out, Jesus said, “Now the Son of Man is glorified, and God is glorified in Him. If God is glorified in Him, God will also glorify Him in Himself and will glorify Him at once. “Children, I am with you a little while longer. You will look for Me, and just as I told the Jews, ‘Where I am going you cannot come,’ so now I tell you. “I give you a new command: Love one another. Just as I have loved you, you must also love one another. By this all people will know that you are My disciples, if you have love for one another.”

Facing the wrath of the Father on our account, Jesus declared Himself glorified, and the Father glorified in Him. This is our security! The Father satisfied with the Son! And Jesus then called the eleven "children" - showing us the meaning of that term as regards spiritual matters.

And then the command. Note this: Jesus did NOT say to return to Moses to learn how to live. He cites a passage from Lev 19:18 but provides a higher standard: love one another as He has loved us. By this - not by keeping the Decalogue (as if you could) - ALL PEOPLE will know we are His disciples. This is the law of the New Covenant: love one another as Christ has loved us. None can approach this nor desire this without the Spirit of God willing and equipping us to do so.

Let all the saints praise Him!