There's an ad I've been hearing a lot lately for a DNA analysis service. The ad says that by getting your DNA analysis you can find out who you are and where you come from. In our post-Enlightenment world, this seems like a rational statement. In the pre-Enlightenment world, it would have seemed laughable. How will a chemical analysis of your chromosomal makeup tell you anything about who you are or where you come from?
Your DNA might tell you whether you're prone to heart disease or type 1 diabetes, and those are important questions. It might tell you about the human migrations that shaped your ancestry, and that's interesting. But we don't gain a sense of who we are and where we come from through chemistry; we get these things through the stories we tell ourselves and the names we are given.
This is why the genealogies are included in both Matthew and Luke, and this is why they're important. Both Matthew and Luke, in very different ways, use the genealogies of Jesus to make statements about him, about the people of Israel, and about us. Matthew uses the genealogy in Matthew 1 to tie Jesus intimately into the history of Israel and to highlight both the noble calling of the descendants of Abraham as well as their ongoing patterns of sin, bigotry, violence, and selfishness. Matthew shows Jesus as the fulfillment of God's promises to Abraham, especially the promise in Genesis 12 that all the nations of the earth would be blessed through Abraham's descendants.
Luke, on the other hand, is telling a different story. He is less concerned about Israel's history and calling and more concerned about Jesus coming for all humanity, coming as a light to all nations. Remember that Luke's primary audience is a non-Jewish man, a Roman official, and Luke deftly tells Jesus' story through his genealogy to include Theophilus. While Matthew traces Jesus' ancestry back to Abraham, Luke carefully goes back even further to Adam, and then to God. Jesus has come for all people. This is one of Luke's primary themes throughout the gospel.
If you read them, you'll find that Matthew and Luke have very different genealogies for Jesus. In fact, Matthew traces Jesus' ancestry through David's son Solomon, down the royal line through the exile in Babylon. Very likely this was Joseph's lineage, as Matthew says he was "of the house and line of David." The version in Luke is quite different, however, and many scholars believe, given the fact that Luke obviously used Mary as a significant source for his gospel and that he acknowledges right at the beginning of the genealogy that Jesus was not biologically Joseph's son, that this list, tracing back through David's son Nathan, was Mary's own ancestry.
Luke uses the genealogy to focus on archetypes, among other things. Luke had been a companion of Paul, and no doubt would have heard and read in Paul's teaching this idea of archetypes that was so familiar to Paul. This is not a way of thinking that we commonly use, so it may seem foreign and unimportant to us. Contrast the way Paul uses Adam and Christ in the last part of Romans 5, for example, and you might begin to see how critical this way of thinking was to Paul. It was well understood in the ancient world that archetypes were critically important to understanding one's self. In our world, we might begin to get the significance of this if we wrapped together our passion for a favorite sports team, our Myers-Briggs type assessment, Strengthsfinders analysis, favorite nickname bestowed by someone we love, and a movie character we deeply identify with. If you take all the impact of all those categories added together in your life, you may begin to get at what it means to have an archetypal identification with a person. This and much more is what Paul is up to in Romans 5 as he talks about being "in Adam" or "in Christ." Paul uses this same tool in Galatians as he talks about Hagar and Sarah and contrasts them. Jesus used archetypal language as well, and frequently we fail to understand the Bible at these points because we are so conditioned to post-Enlightenment ways of viewing truth and meaning.
So Luke is telling us important things. Jesus is the "son of God" both because of his miraculous conception by the Holy Spirit, and also because he is descended down the line of all humanity from Adam. He identifies with God in his "incarnation" but he also identifies with us. He is the ultimate human being. It is this identification with us in our fallen humanity that leads Jesus to "fulfill all righteousness" by coming to be baptized in the Jordan River. It is this identification with us in our fallen humanity that leads Jesus into his mission to rescue us from our alienation and brokenness. And it is this identification, this mission, this stepping into the role of being the New Adam, that brings Jesus squarely up against the forces that have kept the Old Adam in chains. Now Jesus will have to face the consequences of his mission, being tempted in the wilderness. That's where we're headed next.