Ever since the Gospels were written, people have been puzzled by the two differing genealogies of Christ contained in Matthew 1 and Luke 3. Neither genealogy attempts to give a full family tree, identifying all his lines of ancestry. Even so, people are often perplexed. The most obvious difference between the two genealogies is that Matthew’s begins with Abraham and moves forward to Christ, while Luke’s begins with Christ and traces the line backward to Adam.
The next obvious difference is that both genealogies trace Jesus’ lineage back to David, but through different sons. Matthew has Christ descending from David through Solomon, while Luke has him descending from David through Nathan. This is not odd. David had more than one son, and a later individual can be descended from more than one of them.
The question arises, when did the two lines meet up again? The Solomon line runs parallel to the Nathan line until the time of Shealtiel, when they intersect. In Matthew, Shealtiel is described as the son of Jechoniah, and in Luke his father is said to be Neri. How can he have two fathers?
After Shealtiel, both genealogies state that Christ was descended from Shealtiel’s son, Zerubbabel, who was governor of Israel after the Babylonian Exile. Then they diverge again. Matthew traces Christ’s lineage through Zerubbabel’s son Abiud, while Luke traces it through a different son, Rhesa. Again, this is not odd. Zerubbabel simply had more than one son, and Christ was descended from both.
The two lines converge once more in Jesus’ foster father, Joseph. In Matthew, Joseph is said to be the son of Jacob, of the Abiud line, while in Luke Joseph is said to be the son of Heli, of the Rhesa line. So why is Joseph said to have two fathers?
Some have tried to answer this by saying that Luke doesn’t give Jesus’ lineage through Joseph at all, but through Mary. This is not supported by the text. Luke states that Joseph was the son of Heli, not that Mary was the daughter of Heli. In any event, this does not account for Shealtiel’s two fathers.
To explain that issue, one needs to know something about how ancient Jewish genealogies work. Adoption, whether of a child or an adult, was common and affected which genealogical line one was ascribed to. For example, the faithful spy Caleb was biologically the son of a non-Jew named Jephunneh (Num. 32:12), but he was adopted into the tribe of Judah and ascribed to the line of Hezron (1 Chron. 2:18).
Adoption could take place posthumously. The most striking example is what is known as the levirate marriage (from the Latin levir = brother-in-law). If a man died childless, it was the duty of his brother to marry the widow and father a son on behalf of his brother. This son then would be posthumously "adopted" by the dead man and reckoned as his son in the family genealogy.
Adoption is the most probable explanation of Shealtiel’s two fathers. Jeremiah had prophesied that Jechoniah’s (biological) descendants would never sit on the throne of Judah (Jer. 22:30). Thus the legal succession passed to the line of Nathan and Shealtiel. Though biologically the son of Neri, Shealtiel was reckoned as Jechoniah’s son for purposes of the kingly line. It appears that Shealtiel died childless and that his brother Pedaiah fulfilled the obligations of a brother and fathered Zerubbabel (1 Chron. 3:17–19 with Ezra 3:2, etc.).
This solves the first case of two fathers. But what about Jesus’ foster father, Joseph? Here we have more direct information. The second-century historian Julius Africanus, a native of Israel, records information given by Christ’s remaining family in his day. According to their family genealogy, Joseph’s grandfather Matthan (mentioned in Matthew) married a woman named Estha, who bore him a son named Jacob. After Matthan died, Estha married his relative Melchi (mentioned in Luke) and bore him a son named Heli (marrying relatives was common among Jews at this time). Jacob and Heli were thus half-brothers. Heli died childless, so Jacob married his widow and fathered Joseph, who was biologically the son of Jacob but legally the son of Heli (Eusebius, Ecclesiastical History 1:6:7).
There are other ways to reconcile the genealogies. The problem isn’t finding a way to reconcile them but—given the flexibility of ancient Hebrew genealogies—finding which way is correct. More interesting is why the genealogies are different. Matthew stresses Christ as the successor of David and follows the line of kings. Luke stresses Christ as the Son of God and traces the line back to "Adam, the son of God" (Luke 3:38).