Why does Paul never mention Jesus' birth or earthly ministry?
Paul's one message is the death, burial, and resurrection of Christ—the preaching of the cross and the shed blood—not Bethlehem, His birth, earthly ministry, or miracles. Paul reveals the very words of the same Jesus, but from His glorified, ascended position as the resurrected Lord and Savior, not His earthly ministry to the Jew under the law.
Les explains that Paul never mentions Bethlehem, Christ's birth, or His earthly ministry and miracles because Paul's one message is the death, burial, and resurrection of Christ, the shed blood. That is the core of all his epistles. Les also recalls a caller who said we must go by what Jesus said; he cautioned that Jesus' earthly words were spoken to the Jew under the law. When we go to Paul's epistles, Paul reveals the words of the same Jesus from His glorified, ascended position as the resurrected Lord and Savior. This is why Paul never refers back to those earlier earthly details.