"The basic purpose of the genealogy is to identify kinship relationships between individuals, families, and people groups. Marshall Johnson has isolated nine distinct functions that genealogies serve in the Old Testament"
- Demonstrate existing relationships between Israel and neighboring tribes by establishing common ancestors (e.g., the relationship of Lot’s descendants to Israel, Gen. 19:36–38)
- Connecting isolated traditions of Israelite origins into a coherent literary unit by means of an inclusive genealogical system (e.g., the toledot formulas in Genesis [5:1; 10:1; etc.])
- Bridge chronological gaps in the biblical narratives (e.g., Ruth 4:18–22)
- Serve as chronological controls for the dating of key Old Testament events (e.g., the date of the book of Esther in relationship to the Babylonian exile, Est. 2:5–6—although the selective nature of biblical genealogies may compromise the accuracy of the genealogy as a chronological device)
- Perform a specific political and/or military function, as in the taking of a census (e.g., Num. 1:3–46)
- Legitimize an individual or family in an office or enhance the stature of an individual by linkage to an important clan or individual of the past (e.g., Zeph. 1:1)
- Establish and preserve the ethnic purity of the Hebrew community, as in the case of the records found in Ezra and Nehemiah (e.g., Ezra 7)
- Assert the importance of the continuity of God’s people through a period of national calamity (prominent in Chronicles, e.g., the line of David in 1 Chron. 3:17–24)
- Express order, structure, and movement in history according to a divinely prearranged plan (e.g., identifying Haman, the son of Hammedatha, as an Agagite, Est. 3:1, 10).
There may be other purposes but asking questions about each of these is a good start in taking seriously genealogy as a part of the Biblical texts. We don't study them because genealogies are fascinating in themselves, or to construct some super-biblical genealogy, but because 'all' scripture is God breathed, and when read with all of it included it makes us wise for salvation. Genealogies occur relatively frequently in the Biblical narratives and we're overlooking substantial portions of scripture if we omit them. It's not that we expect them to yield meaning in the same way that a sentence in a Pauline letter might, but because they contribute to the literature which God has chosen to use to reveal himself to us.
See also: Ed Goode on the genealogies in 1 Chronicles 1-9