“Whoever claims to love God yet hates a brother or sister is a liar. For whoever does not love their brother and sister, whom they have seen, cannot love God, whom they have not seen. And he has given us this command: Anyone who loves God must also love their brother and sister.” - 1 John 4:20-21
John had been close to Jesus. He had thought, for a long time, that Jesus had promised John would never suffer mortal death. But God keeps all of his promises. In some ways, John died at least twice. Killed by Romans who wanted to silence his cult, John survived and died later, possibly of old age. He wrote this letter probably around the year 98.
Pastoral care is a strong part of any community. Clearly this Christian community had issues and cliques had formed. Maybe not actual siblings, but Christian brothers and Christian sisters. Or maybe actual siblings. But what can one do that is not outmatched by the crucifixion and resurrection of Jesus? Eternal life with God suggests those treasures in life, love, is brought with someone. But division is not part of Heaven, and should not be something someone tries to bring with them.