At this stage of the address, when Jacob was about to explain the serious nature of the sin of rejecting the message of salvation, the Spirit prompted him to employ an impressive gesture. Wherefore he took off his outer garments and shook them before the people. At the same time he prayed God to be his witness on the day of judgment that he had freed himself for responsibility for their iniquities, by delivering the message faithfully. I am, he said, rid of your blood.
We are reminded by this of the instruction our Lord gave his Apostles when he first sent them on a mission. They were not to go as beggars asking for alms, but as ambassadors of a King with favors to bestow. Into whatsoever city or town ye shall enter, he said, ask if there is anybody there who is worthy, and stay there. If they are worthy, your peace will rest on them; if not, it will return to you. And in that case, "when ye depart out of that house or city, shake off the dust of your feet." (Luke 1:12)
"Dust" has several figurative and symbolic meanings in the Scriptures. To sit in the dust and to sprinkle dust on the head was a sign of deep mourning. (Isa. 65:25) was condemned to "eat dust" all the days of his life, he was, in modern language, doomed to an existence of the most degrading nature imaginable. He who, in the Garden of Eden, was the spokesman of Satan, became, as it were, a slave of slaves of the fallen angel. (Pearl of Great Price, Mos. 4:6-7)