A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another. By this all people will know that you are my disciples, if you have love for one another.”
(John 13:34-35 ESV)
Jesus' disciples are to be recognisable by their love for one another. Not only does this seem a laughable description of the church today, they also weren't doing to great on it then - when Jesus says this, Judas has just left to be betray Jesus, Peter is about to deny him, and by the end of the night, most will have fled.
Non-christians can love each other so the love that Jesus is describing here must look different in some way - it should look like Jesus' love for us, which is radical because he loves those who are betraying and deserting him right at that moment. He loves his enemies.
When we’ve seen and experienced Jesus’ selfless, sacrificial, forgiving love for enemies, we start to love others in a selfless, sacrificial, forgiving way, including our enemies, and that’s how the world will recognise the church.