What does John 16:18 mean?

When Christ spoke to His closest followers about dying at the hands of His enemies (Mark 8:31), they often responded with confusion or open rejection (Matthew 16:21–23). In the hours just before His arrest (John 18:1–3), Jesus is reassuring His disciples by promising the presence of the Holy Spirit (John 16:8–13). As part of that, He has again referred to leaving them (John 16:7, 10). However, He also noted that He would be seen, once again, after a short time (John 16:16). The second part of that statement seems to be what mostly concerned the disciples in this moment.

Only after Jesus is resurrected (John 20:19) will these men begin to fully understand all that's happening (John 2:22). The work of the Holy Spirit, in fact, will be key to their knowledge (John 15:26–27). For now, they're baffled, and seem to argue about what these words might mean (John 16:17); the Greek words translated as "They were saying" are in a tense which implies an ongoing process, perhaps a debate or an argument. Still, they don't directly ask Christ about it. Jesus will notice this, however, and offer a helpful perspective (John 16:19–20).