What does John 4:20 mean?

Verses 19 and 20 make it clear that this Samaritan woman is no fool. She was perceptive enough to sense a deeper meaning behind Jesus' first statement (John 4:11). She was willing to press the issue after that (John 4:15). And she was insightful enough not to lie, but to give a less-than-complete response when Jesus asked about her husband (John 4:17). When Jesus reveals that He knows exactly what she has done, she's clever enough to try a distraction. The path she chooses shows she's not only quick-minded, but clever.

This is a common problem in evangelism and in debate. Rather than deal with the point at hand, those looking to duck the issue may try to divert conversation onto something else. This is referred to as a "rabbit hole," or sometimes as a "red herring." It's a path, or a statement, which serves no immediate purpose other than drawing attention away from the current topic.

In this case, the attempted distraction involves a classic argument between the Jews and Samaritans. Samaritans were not allowed to come to the temple in Jerusalem. Their religion taught that true worship could occur only on nearby Mount Gerizim. In a sense, this was something like a "young earth" vs "old earth" or "Calvinism" vs "Arminianism" debate. While the question itself might have been worthwhile, it's not pertinent to what Jesus and the woman are discussing at that moment.

Jesus' response will draw on His prior statement about the woman's sin, as well as parrying her attempted distraction. Instead of letting her avoid the issue, Jesus will show how she needs to confront it: God knows, and He wants people like her anyway.