What does John 8:30 mean?

This short phrase presents a problem for Jesus' earthly critics—in this case, the Pharisees. At the same time, it does not present especially good news for Jesus or His other followers.

Despite their claims to seek truth and to follow God's law, the local religious leaders are mostly concerned with their own power and reputation. Jesus' outrageous claims have not only caused unrest, they have led people to question their leaders (John 7:12–13). Some suspect that the Pharisees have come to believe in Christ (John 7:25–26). If not, they might assume, then these men are too weak to stop a blasphemer. Here, Jesus' words continue to convince members of the crowd that what He says is true. This adds fuel to the Pharisees' burning anger against Jesus.

And yet, the belief many of these people profess is not a saving faith. It might be an agreement, in some sense. But the hallmark of saving faith is to continue in the truth (John 8:12; 1 John 5:1–3). Many, if not most, of the people listening to Jesus in this particular moment will not maintain their support for Him in the coming days. Just as some expressed a shallow sort of "belief" after Jesus fed thousands (John 6:22–25), but then turned away when they did not like His teaching (John 6:66), the people Jesus speaks to now will, for the most part, turn their backs on Him as He continues to confront Pharisaical attitudes towards God.