‘And Moses said, “This is the thing which Yahweh commanded that you should do, and the glory of Yahweh shall appear to you.” '
Moses then informed them that in some way Yahweh intended to manifest Himself to them. As long as they followed his instructions closely, the glory of Yahweh would appear to them. We can imagine the awe and expectancy and reverence with which they watched that day. And if we would know the presence of God with us it can also only be by full obedience.