Charles Ellicott Commentary Exodus 19:17

"And Moses brought forth the people out of the camp to meet God; and they stood at the nether part of the mount." — Exodus 19:17 (ASV)

Out of the camp. —An open space must have intervened between the camp and the “bounds.” Into this Moses led the representatives of the people, so bringing them as near to God as was permitted.

At the lower part of the mount. —In the plain directly in front of the Ras Sufsafeh, and almost under it.