The Bible recognizes the fact that because of extramarital relations lineages are either real (based on the ‘father begat son’ principle) or supposed (based on formulas such as ‘Cain knew his wife and she became pregnant’ or ‘to Enoch was born Irad’). Saint Matthew and Saint Luke offer different genealogies for Jesus because the former is based on the ‘father begat son’ principle while the latter uses the formula ‘Jesus was believed to be the son of’. This is why, for instance, Saint Matthew says Joseph’s father was Jacob, while Saint Luke says it was Heli.
Saint Luke offers an additional generation between Adam and Noah. That Genesis says that Arpachshad begat Shelah, while Saint Luke points out that people believed that Shelah was the son of Cainan, and Cainan the son of Arpachshad, means that Arpachshad first had Cainan, and later had Shelah from his daughter-in-law, Cainan’s wife. Therefore, Judah and Tamar’s relation was not the first one among Jesus’ ancestors between a father-in-law and daughter-in-law.
The genealogy in Saint Matthew, which mentions 4 adulterous women (and one of them is Tamar), ends with, “Jacob begot Joseph, the husband of Mary, of her was born Jesus who is called Christ. The sum of generations is therefore: 14 from Abraham to David; 14 from David to the Babylonian deportation; and 14 from the Babylonian deportation to Christ.”
Since we have to include both the first and the last generation when we count the 14 that go from Abraham to David, we have to do so as well when we count the generations from David to the deportation to Babylon, and from the deportation to Babylon to Jesus Christ. This gives us the division: Abraham/David, David/Josiah, and Josiah/Joseph. Since there are 14 generations from Josiah to Joseph, and Saint Matthew says there are 14 generations between Josiah, who marks the Deportation to Babylon, and Jesus, Joseph and Jesus form part of the same generation, which means that Jacob had Jesus from Joseph’s wife, his daughter-in-law.
There are also 14 generations from Enoch to Abraham, which implies that first every 7 and later every 13 generations Jesus’ male lineage, after crossing again the same female lineage, attracted a special spirit: Enoch, Abraham, David, Josiah and Jesus were all special. The 14 Stations of the Cross suggest that Jesus’ Second Coming – the Messiah – will be a descendant of that special male lineage separated from Jesus several times 14 generations.