Jesus gave us a couple of proofs of discipleship. A disciple in Jesus' day was a person who followed a teacher, received instruction, received assignments, and completed those assignments, learning by doing in the process. So, discipleship is the process of following a teacher, receiving instruction and assignments, completing them, learning and growing. This is similar to the current terms: apprentice and apprenticeship. But discipleship carries a connotation of maturing in character.
So, the first proof of discipleship in Jesus: love one another, as Jesus loved his disciples.
In this instance, Jesus is not saying to love the world. I am not saying that Jesus does not want his disciples to love the world, because I am sure that he does. But proof of discipleship is observable love of God's family for itself.
When you give your allegiance to Jesus, you become one of God's children. You become part of God's family. One part of being in God's family is loving all the parts of God's family.
Because of actions by part of the church, many people feel an us\them attitude in the church. This attitude usually manifests itself in antagonistic, negative, condemning words and actions. Some of God's family believe that such condemnation and harsh criticism does not demonstrate to people that the life Jesus wants us to live is better, and, therefore, does not persuade people to follow him. So, they try to diminish the line between us and them. But there is an us\them division. And Jesus put it there. You are either his disciple, or you are not. You are either his child and in his family, or you are not.
But Jesus focused on the nature of what defined the division. He did not call his disciples to invest themselves in political, moral, or cultural change by political, cultural, or moral means. He called his disciples to foment a spiritual and existential revolution.
Jesus' first-century family blew the doors off their world. And we have seen flashes since: the Methodists in 17th century England, the church in Communist China, various church planting movements around the world today, etc. But overall the modern day family of God limps along, because it uses the weapons of the world, instead of the weapons of God.
Weapon #1: A genuine relationship with the living, creator God, who demonstrated his love for people on the cross.
Weapon #2: A genuine love for God's family; and by extension, the love of God's family for the rest of the world.
And that lost is expressed in imitation of how Jesus loved Peter, John and the others.