Charles Ellicott Commentary Exodus 19:20

"And Jehovah came down upon mount Sinai, to the top of the mount: and Jehovah called Moses to the top of the mount; and Moses went up." — Exodus 19:20 (ASV)

On the top of the mount. —On the summit of the Ras Sufsafeh, not on the Jebel Musa, which is out of sight from the plain of Er Rahah.