What does Mark 6:11 mean?

"Testimony" is from the Greek root word marturion. This means "a witness, or someone who attests to the accuracy and authenticity of something or someone else." In Mark 1:44, Jesus tells the leper to go to the priest as proof that he is clean and Jesus has healed him. Later, Jesus will tell the disciples that their coming persecution will stand as a witness to the gospel message. And James says that worldly possessions are a testimony of our priorities (James 5:3).

Pious Jews were known to shake out their robes when leaving a Gentile town, as if protecting themselves from being contaminated by false beliefs. By shaking the dust from their feet, the Twelve show that Jews who reject Jesus' gospel are as lost as the Gentiles who do not know God at all. They testify that the people have chosen a different path and that the Twelve are not responsible for their choices. Paul and Barnabas do this in Pisidia (Acts 13:51), and Paul goes so far as to shake out his garments when the Jews in Corinth revile him (Acts 18:5–6).

Jesus uses more colorful metaphors in the Sermon on the Mount: "Do not give dogs what is holy, and do not throw your pearls before pigs, lest they trample them underfoot and turn to attack you." (Matthew 7:6). The point of this lesson is the need to discern when someone has hardened their heart against the gospel. We tend to think if we can find just the right argument, we can convince the antagonist. But Jesus tells us to step back. Before sending them out, Jesus tells the Twelve, "The harvest is plentiful, but the laborers are few" (Matthew 9:37). If we cannot differentiate between the good soil and the bad (Mark 4:1–9), we will waste a lot of time trying to reach the apathetic while the seeking remain unreached.