In the final moments before the crucifixion, Jesus told the disciples about how the world hates Jesus and how there would be persecution towards the disciples. Those don't sound like good news, so why did Jesus say these things? Jesus declared that he said these things because they would "not be made to stumble" (16:1). In other words, by alerting them about the upcoming persecutions ahead of time, Jesus is giving them prep time so they can be prepared when said persecutions happened.
Jesus also elaborated on the persecutions themselves. In particular, one of them would be bans from entering synagogues (16:2), a place normally to meet with other people. The synagogue ban likely puts social pressure in, but the ban is also in part because people think they are serving God (16:2) -- especially with Pharisees' issues with Jesus. However, Jesus told the disciples that the persecutors don't really know Jesus or even the Father (16:3). In particular, Jesus is closely connected with the Father, who is the very God the persecutors think they are serving.
At the start of Jesus's ministry, there wasn't much persecution and Jesus was with them, but now there is a lot of pressure -- while Jesus would be away on a cross! However, Jesus's words are meant to help the disciples be prepared when big trouble strikes.