On the year’s shortest day, hundreds of Israelis ventured deep into the desert to witness a strange natural phenomenon atop an ancient pilgrimage site that some argue is where God spoke to Moses. The mountain kept its secrets for centuries, its air of sacred mystery enhanced by a remote location in the Negev Desert in southern Israel. But one day last week, hundreds of Israeli adventurers headed deep into the wilderness to reach Mount Karkom, determined to get closer to answering a question as intriguing as it is controversial: Is this the Mount Sinai of the Bible, where God is...