There were seventy people in the family of Jacob living in Egypt. Over the course of 430 years (Ex. 12:40) this large family has now grown to a considerable number known as the people or children of Israel.
Under the leadership of Moses, the people of Israel have come to the wilderness of Sinai and camped at the foot of a mountain. This is about seven weeks since the exodus from Egypt (Ex. 19:1) and this occasion is the fulfillment of what God said to Moses when He called him to lead His people (cf. Ex. 3:12).