Immediately after commanding the disciples to love one another, Jesus warns them that the world may hate them. He reminds them that it hated him first and that a servant is not greater than his lord.
The warning places future rejection within their identification with Jesus.
In John, 'world' can refer to humanity, the created order, or more specifically the human system organized in resistance to God; the context determines the sense. Here it does not mean that every non-Christian individual will personally hate every disciple. The language concerns a sphere of opposition to Jesus. In an honor-shame culture, rejection, public hostility, and loss of belonging could carry serious social consequences in addition to physical danger.
The context keeps the warning from becoming either paranoia or surprise. Jesus does not teach the disciples to hate outsiders; he has just commanded love.
He tells them that allegiance to him may place them at odds with prevailing loyalties, and that such rejection follows the pattern already experienced by their master.