What is the significance of the recurring phrase “These are the generations” (the first instance of it being at Gen 2:4)?

This phrase, the toledoth (“generations”) formula, precedes one of a series of connected accounts. Genesis 1 does not begin with this phrase, but from here until the end of the book, all the various accounts are included these sections, some rather short and others chapters long. The word תּוֹלְדָה or toledoth means “generations,” or, it seems, something like “an account of how something came about” and usually “an account of the generations following” some person such as Noah. Each family was said to have a “head” for his generation; so we might say that the sections recount the story of a family. We will be returning to this topic as new toledoths appear.