In the words of Malachi which the Savior ask the Nephites to record, we find the following: "But who may abide the day of his coming, and who shall stand when he appeareth? For he is like a refiner's fire, and like fuller's soap" (3 Nephi 24:2).
The art of fulling, cleansing and bleaching cloth was of importance because of the high cost of clothing and the need to cleanse the fibers of their natural oil or gums before dying. In some places the fuller was also the dyer.
It was customary for a fuller to work outside a town within reach of water in which clothes could be cleaned by treading them on a submerged stone. Hence the fuller was characteristically called a "trampler" (Heb. Kabas). At Jerusalem the locality outside the East wall where garments were spread to dry in the sun was called the "fuller's field" (2 Kings 18:17; Isaiah 7:3; 36:2). [Tyndale House, The Illustrated Bible Dictionary, Vol. 1, p. 128]
It is interesting that while we don't know whether the Nephites knew what the term "fuller's soap" mean't before the Savior's visit, we are told that, at this time, Jesus "expounded" the words of Malachi unto them (3 Nephi 24:1), so the cultural meaning would have been clearly brought out to them.