Our Mishna on Amud Beis teaches:

If a man has two wives with identical names and he writes a bill of divorce intending to divorce the older one but then changes his mind, he may not use that bill to divorce the younger one.

The Hon Ashir in the Mishna notes that the description of a case where the bill is written to divorce the older wife, rather than the reverse scenario or wives of the same age, is essentially unnecessary. However, the Mishna presents this case to highlight the tendency for jealousy and discord between the older and younger wives, which could lead to divorce.

This teaching is based on a passage in Gemara Megillah 13a:

"And when the virgins were gathered together the second time, Mordecai sat in the king's gate." Achashveirosh sought advice from Mordechai on how to compel Esther to reveal her family and nationality, not knowing Mordechai was her uncle. Mordechai’s advice to Achashveirosh was: "A woman is jealous of the thigh of another woman. Therefore, you should take additional wives, and she will feel jealous and insecure, making her more compliant." But even so, Esther did not reveal her origins, as it is written: "Esther had not yet made known her kindred nor her people."

Beis Yaakov (Vayetze 67) explains this principle in the context of Rachel's infertility and divine intervention. Despite Rachel's plea for Yaakov to pray for her, his prayers were blocked due to some imperfection. Yaakov could only align with the pure will of Hashem, so he could not pray for something undeserved. This is the true meaning of Yaakov's response in Bereishis 30:2, "Am I to be in the place of God?"—meaning, I cannot defy His will. When Rachel offered her maidservant to bear children in order to fulfill the mitzvah of producing the Twelve Tribes, it was a complete contradiction to the norms of jealousy. This act served as a rectification and repair of her character deficiency, and subsequently, their prayers were no longer hindered.

It is an interesting concept that for certain righteous individuals, their unwavering commitment to God's will can actually hinder their ability to pray for mercy or special consideration. They impose upon themselves the requirement to correct their character before their prayers can be heard.