Musar su Genesi 38:15

This is the deeper significance of the kingdom of David, which at first glance does not appear to have been rooted in holiness. Simply consider Yehudah's involvement with Tamar whom he thought to be a harlot; or, if you will, think about Ruth, a descendant of an incestuous union between Lot and his daughter. Even Ruth's joining Boaz at night was not exactly the act of a model of chastity that we would have expected. If all these precedents did not disqualify David from becoming the role model of the eventual Messiah, we need not marvel at the eventual purification of those descendants of Esau who will still exist when the Messiah will be crowned king. All these apparently accidental happenings were part of G–d's plan. The tortuous developments which led to the emergence of David and eventually to the Messiah are an example of how eventually all the חצוניות, people and forces outside the realm of holiness, will be turned "outside in," and be restored to their original sacred root.