“So Moses went down from the mountain.” This is Moses’ second time down Mount Sinai, and he brought more instructions from Yahweh down to the people. He had gone up for a second time in Exodus 19:8. Moses’ next (and third) trip up Mount Sinai is in Exodus 19:20.
[For more on Moses’ seven trips up and down Mount Sinai, see commentary on Exod. 19:3. For more on God speaking directly to Israel with a loud voice from the top of Mount Sinai, see commentary on Exodus 19:9.]