What does John 16:2 mean?

Much of Jesus' teaching flew in the face of legalists like the Pharisees (Matthew 5:20). His words were not, at all, contradictory to the Word of God (Matthew 5:17–19)—but religious leaders were not enthusiastic about His message (John 11:53). Jesus is preparing His followers to maintain faith in the face of persecution (Matthew 5:10–12; John 16:1). Instead of reacting in fear or panic, believers should respond to hardship by remembering that God knows exactly what is happening.

In the most immediate sense, those who followed Christ were subject to excommunication by their fellow Jews (John 9:22; Acts 8:1–3). In a broader sense, the full gospel is offensive to the arrogant, fallen human mind (Matthew 11:6; 1 Corinthians 1:18). People rejected the messages of John the Baptist (Matthew 11:18) and Jesus (Matthew 11:19), for entirely opposite reasons. In the same way, self-labelled "religious" people may dismiss biblical Christians as too strict, or too loose, and "put [them] out" as a result.

The most extreme version of this persecution is death. Some will be so opposed to the gospel, and so blinded by false religion, that they will see the murder of Christians as an act of righteousness. That might involve a literal deity, as with Islamic persecution of believers. The Greek phrase here is laterian prospherein—literally meaning "an offering of service." The root word lateria is the same one used in Romans 12:1 to describe "service of worship" (NASB).

The passion that leads people to kill Christians can also be a false god, such as the Nazi or Communist ideals which have also led to the deaths of many Christians. Regardless of specific motives, Jesus is warning that opposition to His truth (John 14:6) can be both deadly and driven by intense emotion.