Moses experienced his call to lead the enslaved Israelites out of Egypt when he saw on Mount Sinai a bush apparently on fire but never becoming burnt up (Exod. 3: 2). He accepted the vision as a promise from God to be faithful; and in a gesture of reverence in the presence of the holy he removed his sandals, as Muslims do today when they enter a mosque. The natural cause of the burning phenomenon may have been a discharge of atmospheric electricity on pointed objects during a storm.