וַֽיִּמְצָאָ֞הּ מַלְאַ֧ךְ יְהוָ֛ה עַל־עֵ֥ין הַמַּ֖יִם בַּמִּדְבָּ֑ר עַל־הָעַ֖יִן בְּדֶ֥רֶךְ שֽׁוּר׃
האָט אַ מלאך פֿון גאָט זי געפֿונען בײַ אַ קװאַל װאַסער אין דער מדבר, בײַ דעם קװאַל אױפֿן װעג קײן שור.
Abarbanel
The tenth question: What is this, that the angel of God called to Hagar and spoke with her, when she was not suited for prophecy? And behold the first time that the angel spoke with her (Genesis 16:7-8), it was for the sake of Avraham, to return her to his house; since she had fled from there. But here it would have been enough for God to open her eyes, as He did, and she would have seen the well and given the youth to drink from it. And if the speech was on account of the youth, who was a son of Avraham, why did the angel not speak to the youth himself - as he was already seventeen years old or more - but rather speak to Hagar the Egyptian? And behold I will explain the verses of this section in such a way that all of these questions will be solved.
Tur HaArokh
הנה אמתי בלהה, בא אליה ואבנה גם אנכי, “here is my maidservant Bilhah, sleep with her and I too will be built through her (child).” Sarah, when suggesting that Avraham sleep with Hagar, had phrased it differently, saying “perhaps I will be built up though her.” (Genesis 16,7). Rachel appeared certain that Bilhah would have a son. The reason for her feeling certain that she would succeed was that Avraham had not yet been told by G’d that he would have a son by Sarah. Rachel, having revealed to her sister the secret code between her and Yaakov so that she would not be embarrassed under the wedding canopy, was certain that this merit would work in her favour now. Her preparedness to allow a competitor to sleep with her husband would, she was sure, produce in the desired result. Some commentators believe that Rachel’s certainty was based on the extra letter ה in Bilhah’s name, this being an allusion to offspring as per הא לכם זרע, or כי בי-ה ה' צור עולמו, this world having been created under the aegis of the letter ה. Rachel, רחל was the only of one of the matriarchs who did not have the letter ה in her name. She meant to make up for this deficiency by giving בלהה to her husband as her alter ego.
Redeeming Relevance; Genesis
A thorough examination of the text reveals other flaws in Hagar’s character besides the feelings of superiority mentioned earlier. Such an examination of Bereshit 16:7-14 reveals Hagar’s problematic reticence to listen to the angel(s) sent to direct her back to Avraham’s home. Whether it indicates a multiplicity of angels or not, the Torah’s repeating “And the angel said to her” does indicate some sort of pause after each phrase, as if we are expecting Hagar to react.9Many commentators point this out. See, for example, Abarbanel and Malbim. In other words, each statement should be enough to get Hagar to return back home, but she resists until the final promise, that her son’s character will somehow compensate for her situation. This is in marked contrast to Avraham’s immediate acquiescence to the Divine demands placed upon him to sacrifice his son.