In this passage it’s helpful to remember that Jesus is not speaking to unbelievers here – but that His audience is the 11 disciples and by extension all believers seeking to live in discipleship.
v5: At first I thought this was just a restatement that we can do nothing of worth without the power of Jesus, and I suppose it is, but it also clarifies for the first time that THE disciples (and all believers seeking to live in discipleship) are represented by the branches. This verse also repeats and emphasizes that disciples have a choice to continue to abide or not to abide.
v6: Jesus gave two classes of believers in v2 – those that dry up because they’re not abiding in Jesus and bearing fruit; and those that do abide and bear fruit. Jesus now switches from talking about the second group and talks about the first group.
If a believer stops abiding, that branch is thrown away – which is a picture of being outside of fellowship with Jesus. The branch/believer stops abiding in fellowship first, then the vine/Jesus follows through by removing fellowship. When that branch is then thrown away, it dries up – a loss of spiritual vitality. These branches are now not good for anything, so they’re gathered up and cast into the fire of discipline.
This whole picture has been so misunderstood as talking about unbelievers going to hell because of the knee-jerk reaction to think that every reference to fire is a reference to hell – most times the Bible is referring to discipline here on the earth in this life.