Why does Mary's genealogy go all the way back to Adam?
Mary's genealogy goes back to Adam because it traces the physical bloodline of Christ, and all people are sons of Adam. By contrast, the royal lineage in Matthew stops at Abraham, since the promise of a king comes through the Abrahamic covenant.
Les explains that Luke chapter 3 presents Mary's genealogy, which goes all the way back to Adam, who was the son of God. This is because Mary's line is the bloodline of Christ, and since we are all sons of Adam, it must trace to Adam. However, with regard to His ascension to the royal throne, the genealogy only goes back to Abraham, because the promise of a king is found in the Abrahamic covenant, not before Abraham. Les notes how accurately Scripture keeps everything.
Which was the son of Enos, which was the son of Seth, which was the son of Adam, which was the son of God.