Among the Hebrews, circular spots of hard ground were used, as now, for the purpose of threshing corn. After they were properly prepared for the purpose, they became permanent possessions. One of these, the property of Oman the Jebusite, was on Mount Moriah (First Chronicles xxi, 15 28). It was purchased by David, for a place of sacrifice, for six hundred shekels of gold, and on it the Temple was afterward built. Hence it is sometimes used as a symbolic name for the Temple of Solomon or for a Master's Lodge. Thus it is said in the instructions that the Freemason comes "from the lofty tower of Babel, where language was confounded and Masonry lost" and that he is traveling "to the threshing-floor of Oman the Jebusite, where language was restored and Masonry found."
The interpretation of this rather abstruse symbolic expression is that on his initiation the Freemason comes out of the profane world, where there is ignorance and darkness and Confusion as there was at Babel, and that he is approaching the Masonic world, where, as at the Temple built on Oman's threshing floor, there is knowledge and light and order.
- Source: Mackey's Encyclopedia of Freemasonry