Why does it say "we all have one father"?
Radak: Now the Navi comes to rebuke them for another Aveirah - they married Nochriyos, like it says in Ezra Perek 9. Even one who had a Jewish wife, he married a Nochris and loved her more than the first. Therefore, it says we all have one father - we are all Bnei Yakov, men and women. Why does one betray his brother?
Malbim: Now he comes to rebuke them for marrying Nochriyos. There are two evils in this. (a) They married "Bas El Nechar" (11). (b) The Nochriyos were the mistresses, and the [men] viewed the Jewish wives as slaves of the Nochriyos. Also refer to 2:10:2:2.
Why does it add "one G-d created us"?
Radak: We believe in one G-d who created us, unlike the gods of the nations, from which you marry women.
Malbim: Taking wives from their nation was a proper match. One reason is kinship - they all descended from the chosen Avos. Another reason is, all believe in one G-d. They gave birth to Kadosh seed like themselves. Marrying Bas El Nechar blemished the unity of the family, and unity of Emunah. They are from different families, and believe in different gods.
How did one betray his brother?
Malbim: Marrying Bas El Nechar blemished the unity of the family.
What is the Bris of our fathers?
Rashi: The Bris that Hashem made with our fathers at Sinai.
Radak: It is a Bris not to betray one's wife. Avraham, even though he did not have children from Sarah, he did not betray her to marry another wife, until she willingly said "Bo Na El Shifchasi Ulai Ibaneh Mimenah" (Bereishis 16:2). Also Yitzchak, even though Rivka was barren, he did not marry another. Also Yakov did not willingly marry another wife in addition to Rachel and Leah, until they willingly gave to him.
Malbim: Marrying Bas El Nechar blemished the unity of Emunah and profaned the Bris of our fathers with the one G-d.
