In the genealogies of Christ in the Gospels of Luke and Matthew, we observe notable discrepancies which have puzzled scholars throughout history, giving rise to various interpretations. The primary points of difference include: firstly, in Matthew's lineage, Joseph's father is identified as Jacob (Matt. 1:16), whereas in Luke's version, it is Eli (Luke 3:23). Secondly, the paternal lineage of Salathiel and Zerubbabel differs between the two accounts; Matthew claims Salathiel is the son of Jechoniah (Matt. 1:12), while Luke states he is the son of Neriah (Luke 3:27), and similarly, their descendants diverge with Matthew listing Abiud as Zerubbabel's son (Matt. 1:13), while Luke names Risaiah (Luke 3:27).
Thirdly, the genealogies differ regarding Joseph's descent from David: Matthew traces it through Solomon (Matt. 1:6-7), while Luke traces it through Nathan (Luke 3:31). Furthermore, the names and the number of individuals listed between David and Salathiel (Matt. 1:7-12, Luke 3:31-27) and between Zerubbabel and Joseph (Matt. 1:13-16, Luke 3:27-23) do not align in either sequence or quantity.
Several explanations arise for these discrepancies: one suggests that Matthew provides the genealogy for Joseph, while Luke offers that of Mary, both being descendants of David through different lines. However, this conflicts with Luke’s explicit reference to tracing Joseph's lineage as well (v. 23), and it was uncommon to maintain genealogies along the maternal line, despite Mary's Davidic heritage. Another proposition is that both genealogies refer to the same individuals, albeit with varied names, reflecting the Jewish tradition of multiple names for the same person. Yet this argument fails to account for the distinct lines from David and the differing counts of individuals in both genealogies.
A more plausible explanation relates to the law of levirate marriage, which stipulates that a brother or nearest kin of a childless deceased man should marry his widow to preserve the family line (cf. note on Matt. 1:12). Children from this union would be perceived as having dual paternal identities: one biological and the other, legal. Thus, Matthew names Salathiel as the son of Jechoniah (the childless), according to the law, while Luke identifies his biological father as Neriah, who carried on Jechoniah’s line. Zerubbabel, the adopted son of Salathiel, fathered Abiud and Risaiah, with Matthew tracing descent from the former and Luke from the latter. This distinction extends back to their respective lines from David, with Matthew establishing lineage through Solomon and Luke through Nathan, leading to their identification of Jacob and Eli as Joseph’s fathers: Eli, who died childless, had Jacob, his nearest relative, restore his line through marriage to his widow, resulting in the birth of Joseph, who was biologically Jacob’s son, yet legally Eli’s.
This genealogical interpretation originated with Julius Africanus in the second century, who purportedly obtained it from relatives of the Virgin Mary (Eusebius, Church History 1.7). This rationale is considered the most credible and has gained acceptance among numerous Church fathers and theologians. Such applications of levirate marriage laws might have been common during periods of scarcity for the house of David, particularly during the Babylonian exile and leading up to Christ's coming, when the Davidic lineage had ceased reigning in Jerusalem.