Mark 6: Dust to Testify
And whosoever shall not receive you, nor hear you, when ye depart thence, shake off the dust under your feet for a testimony against them. Verily I say unto you, It shall be more tolerable for Sodom and Gomorrha in the day of judgment, than for that city. (verse 11)
The dust will rise in the day of judgement to testify against those who reject the gospel, for our part, we preach Christ.