“Now go, lead the people.” This points to Moses’ sixth trip down Mount Sinai, which is not expressly stated in the Bible but which we know happened because Moses shows up with the people who are down at the base of Mount Sinai. [For more information on Moses’ seven trips up Mount Sinai, see commentary on Exod. 19:3].
“in the day when I visit, I will visit their sin upon them.” When God “visited” someone, He intervened in their life, and He could intervene for the better or for the worse. God is a righteous God, and He holds people accountable for their actions. Although the word “visit” could be translated “punish” here, and many versions do that, the word “visit” shows that God does not just “punish,” He visits and evaluates the situation and then acts accordingly. In this case, “I will visit their sin upon them” means that God will punish people for their sin. [For more on “visit,” see commentary on Exodus 3:16 and 20:5].