“and 70 of the elders of Israel went up.” Moses and some of the main leaders of Israel went part way up Mount Sinai. They did not go all the way up the mountain, only far enough to see that God was indeed on the mountain (Exod. 24:1-2; 9-11).
[For more information on Moses’ seven trips up Mount Sinai, see commentary on Exod. 19:3].