How do we know that the Luke 3 lineage is Mary's? We do not know it for certain, but that conclusion is the most reasonable. One factor is, again, the purpose of this particular gospel. Luke wrote primarily to Gentiles, and he stresses Jesus' humanity throughout his book. The evangelist thus gives our Savior's natural, biological family tree to show He shares humanness with the common man. He is not just the Jews' Messiah, but He is also the Gentiles' Messiah! So Luke's genealogy goes all the way back to Adam, rather than stopping at Abraham as Matthew's does.
Another factor is that Luke had to deal with a virgin birth. What a unique situation for a genealogist! Luke had to determine, therefore, what points would matter to a Gentile. Would he be concerned with Jesus' Davidic ancestry? Not initially. Would he care that Jesus is a Jew and an Israelite? Maybe. Would he desire to know if Jesus was a man like he was? Certainly! Thus, Luke would record a line of descent that showed His universality to every man, and this would go through Mary, Jesus' link to humanity.
Some raise objections to this on the basis of verse 23, particularly because it says, "Joseph, the son of Heli." Notice, though, that Luke does not use the word "begot" as Matthew does. In fact, he uses no word at all, just a marker to denote possession. So the phrase literally says, "Joseph, of Heli."
Some say, then, that this connotes a levirate marriage because Matthew says Joseph's father was Jacob. Levirate marriage, however, was fairly rare, so this is an unlikely stretch. Others argue that this is Jesus' "priestly" lineage, but this is even less probable, since it shows Judah, not Levi, as an ancestor (see Hebrews 7:14).
Bullinger, in his Companion Bible, gives a more likely explanation: "Joseph was begotten by Jacob, and was his natural son (Matt. 1:16). He could be the legal son of Heli, therefore, only by marriage with Heli's daughter (Mary), and be reckoned so according to law." At that time, Jewish law traced inheritance and descent through the male, not the female line. Thus, Luke 3:23 would be clearer if translated as, "Joseph, the son-in-law of Heli," or "Joseph, the legal son of Heli."
No matter which we choose, it traces Heli's line from that point on back to Nathan, the son of David. There is no stigma or disqualification in Solomon's name being absent from the list. In messianic terms, David's name is the vital one.
Richard T. Ritenbaugh
Why Does Jesus Have Two Different Genealogies (Matthew 1:1-16; Luke 3:23-38)?
These two chapters, both giving genealogies of Jesus, at first appear to be contradictory. Actually, however, they complement each other.
The genealogy in Matthew 1 is clearly that of Joseph, Mary's husband. Matthew records it for legal purposes. He is writing to prove to the Jews that Jesus is the Messiah, and the Jews' custom in keeping records is to trace descent through the father. Legally, the Jews of Jesus' day looked on Jesus as a son of Joseph (John 6:42). Also, Joseph's lineage is given to emphasize the fact that Jesus had been born of a virgin. Because of a curse that God placed on one of Joseph's ancestors, Jesus could never sit upon the throne of David if Joseph had been His natural father.
Jechonias (Matthew 1:11-12), called Coniah in Jeremiah 22:24-30, was so evil God cursed him and his descendants, saying, "Write this man down as childless, . . . for none of his descendants shall prosper, sitting on the throne of David, and ruling anymore in Judah" (verse 30). Jeconiah, as his name is spelled in the Old Testament, had children (I Chronicles 3:17), but he was childless insofar as none of his descendants ruled as king over Judah.
How, then, could Jesus be a descendant of David and qualify to sit on the throne? Enter the genealogy in Luke 3, which is Mary's. According to Jewish usage, Mary's ancestry is given in her husband's name. The original Greek merely says Joseph was "of Heli" or Eli (verse 23). In fact, since Joseph's father is said to be Jacob in Matthew 1:16, Heli is most probably Mary's father. Joseph, then, is his son-in-law.
Unlike Joseph's lineage, there was no block in Mary's genealogy to Jesus sitting on the throne of David. Mary's descent from David comes through his son Nathan, not Solomon or one of David's other children (Luke 3:31). To fulfill His promise to establish David's throne forever, God honored Nathan by making him the ancestor of the promised King who would sit on David's throne throughout eternity (Luke 1:31-33).
But how could Mary transmit David's royal inheritance—the right to the throne—to her Son, since all inheritances had to pass through the male line? According to Israel's law, when a daughter is the only heir, she can inherit her father's possessions and rights if she marries within her own tribe (Numbers 27:1-8; 36:6-8). There is no record that Mary had any brothers to inherit her father's possessions and rights. Thus, Joseph became Heli's heir by marriage to Mary, inheriting the right to rule on David's throne, even over Judah. This right then passed on to Jesus.
Both genealogies had to be recorded to establish Christ's right to rule on David's throne. Joseph's genealogy shows that Christ was a legal descendant of Jeconiah and thus legally could not sit on the throne of David in the nation Judah by inheriting the right solely through Joseph.
Further, the genealogies prove the virgin birth: The curse on Jeconiah's line would have passed on to Christ if He were Joseph's natural son, but He was not—He was the Son of God the Father, begotten by the Holy Spirit.
Jesus was Mary's son descended from Nathan. Jesus can inherit rule over Judah because of Mary's marriage to Joseph, whose genealogy shows he was Heli's son-in-law.
Christ's Female Ancestors
Why Three Kings Are Missing From Matthew 1
Was Jesus a Jew (Matthew 1:1-16)?
Other Forerunner Commentary entries containing Luke 3:23: