Sforno on Deuteronomy 7:6/ספורנו על דברים ז׳:ו׳

1כי עם קדוש אתה, and it is not appropriate for you to desecrate your sanctity through women committed to alien deities, who will bear you children that are already genetically corrupted. It is this that the prophet Maleachi 2,11 had in mind when he spoke of כי חלל יהודה קדש ה' אשר אהב ובעל בת נכר,”for Yehudah profaned what is holy to the Lord, what He desires, by sleeping with daughters of alien gods.”

2בך בחר, as distinct from corrupt seed; our sages referred to this concept as “the benevolent presence of G’d is present (rests on) only families who are genetically offspring of families with good Jewish pedigrees.” (Kidushin 70)