Moses compares Yahweh to the rising sun. Alternate translation: "When Yahweh came from Sinai, he looked to them like the sun when it rises from Seir and shines out from Mount Paran" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Other possible meanings are 1) "In his right hand were flames of fire" or 2) "He gave them a law of fire" or 3) "He came from the south, down his mountain slopes."