Commentary for I Samuel 17:55

Whose son is this youth. Our Rabbis said, "Did he not recognize him? Is it not stated, "He loved him very much and he became his arms bearer"?²⁹Above 16:21. Ralbag suggests that Dovid would now marry his daughter and Shaul therefore inquired about his genealogy. But, he saw him behaving in a kingly manner. Shaul said, 'If he comes from the family of Peretz, he will become king, for the king may break fences to make way for himself, and no one may object. If, however, he comes from the family of Zerach, he will become an important person. Do'eg said to him, 'Before you ask whether or not he is descended from a family which qualifies him for the throne, ask whether or not he is qualified to enter [by marriage] into the congregation [of Yisroel], because he is descended from Rus the Mo'avite.' Avneir responded to him, 'We have learned that an Ammonite [is forbidden]³⁰Devarim 23:4. but not a female Ammonite [the same holding true for a female Moavite].' So Doeg said to him, 'If so, only a male momzer and not a momzeres [=female momzer] should be foridden.' He replied, 'It is stated here, "because they did not meet you with bread and water,³¹Ibid., verse 5. and it is not customary for a woman to do so."' He said to him, 'Men should have met men, and women should have met women [with bread and water].' Avneir became silent. Then Shaul said to him": Ask whose son this young man is. Above it is written 'הַנַּעַר'³²Verse 55. and here it is written 'הָעָלֶם'. He said to him, "This law has escaped your memory [נִתְעַלְּמָה]. Go out and ask in the house of study," as it is stated in [Maseches] Yevomos.³³