Deuteronomy 4:10 (ESV)

10 how on the day that you stood before the LORD your God at Horeb, the LORD said to me, ‘Gather the people to me, that I may let them hear my words, so that they may learn to fear me all the days that they live on the earth, and that they may teach their children so.’

Moses calls to mind for Israel how on their behalf he stood before the Lord at Horeb. There the Lord instructed him to assemble Israel, for the purpose of meeting God by means of his word.