What does Exodus 6:21 mean?

Aaron married Elisheba, the daughter of Amminadab and sister of Nahshon. They had four sons: Nadab, Abihu, Eleazar, and Ithamar. Exodus 6:21 - Modern Text Bible

(Aaron's marriage and children are listed because his family becomes the priestly line. Elisheba's family is also important among the Israelites.)