Same reason its relevant today. Jesus the miracle worker is not enough. For Him to be of God He has to be the promised Messiah. He has to fit the prophets description. Is this really all youve got?<quoted text>
If that were so, it would be completely irrelevant whether Jesus could be actually, legally traced back to David. Why would anybody in the Greek and Roman world care?
CHristianity in the 80s was still a primarily Jewish sect, and the gospel writers clearly felt the need to establish Jesus' bona fides with regard to a supposed "Messiahship."