What does Exodus 6:19 mean?

Merari was the third son of Levi (Exodus 6:16). His two sons, Mahli and Mushi, complete the brief description of the clans of Levi (Exodus 6:16–18). Merari was among the descendants who entered Egypt with Jacob and his family (Genesis 46:8, 11). In the first census after the exodus, 6,200 Merarites were listed among the males one month old and upward (Numbers 3:34). They helped to maintain the tabernacle (Numbers 3:36–37). Their full list of duties in the tabernacle is found in Numbers 4:29–33.

The descendants of Merari would later inherit twelve cities beyond the Jordan (Joshua 21:7, 34–40). The Merarites are specifically mentioned as taking part of the cleansing of the Jewish temple in the time of Hezekiah (2 Chronicles 29:12) and the reign of young King Josiah (2 Chronicles 34:12). According to a non-canonical book, Merari also had one daughter named Judith.