"These were the heads of their families: The sons of Reuben the firstborn son of Israel were Hanok and Pallu, Hezron and Karmi. These were the clans of Reuben. The sons of Simeon were Jemuel, Jamin, Ohad, Jakin, Zohar and Shaul the son of a Canaanite woman. These were the clans of Simeon. These were the names of the sons of Levi according to their records: Gershon, Kohath and Merari. Levi lived 137 years." NIV translation
This family tree is given so that we can know who these messengers of God's deliverance were. The sons of Reuben and Simeon are listed just so we get to the third son of Israel which was Levi. The Levites would be the chosen ministers of the people and it began here with the calling of Moses and Aaron.
"The sons of Gershon by clans, were Libni and Shimei. The sons of Kohath were Amram, Izhar, Hebron and Uzziel. Kohath lived 133 years. The sons of Merari were Mahli and Mushi. These were the clans of Levi according to their records. Amram married his father's sister Jochebed, who bore him Aaron and Moses. Amram lived 137 years." NIV translation
We notice that the age of the men is given when they live longer than 100 years.
This is common in the Old Testament. We see that Moses and Aaron were the fourth generation of Levites and are reminded that, throughout the Bible, the number four is associated with trials and testing.
"The sons of Izhar were Korah, Nepheg and Zikri. The sons of Uzziel were Mishael, Elzaphan and Sithri. Aaron married Elisheba, daughter of Amminadab and sister of Nahshon, and she bore him Nadab and abihu, Eleazar and Ithamar. The sons of Korah were Assir, Elkanah and Abiasaph. These were the Kohathite clans. Eleazar son of Aaron married one of the daughters of Putiel, and she bore him Phinehas. These were the heads of the Levite families, clan by clan." NIV translation
The list continues down to the children of Aaron who would be the first members of the priesthood of God. We will look at many of these characters more as we progress in our study of the Bible.