Genesis 16:4

“And he went in unto Hagar, and she conceived, etc.] The formality of the marriage being over, he enjoyed her as his wife, and she immediately conceived by him: and when she saw that she had conceived; when she perceived that she was with child: her mistress was despised in her eyes; she thought herself above her, and treated her as her inferior, with contempt, and reproached her for her barrenness, as Peninnah did Hannah, (<090106>1 Samuel 1:6,7); and it was the more ungrateful, as it was at the motion of her mistress that she was given to Abram for wife.”

“- The Birth of Ishmael 1. הנר hāgār, Hagar, “flight.” Hejrah, the flight of Muhammed. 7. מלאך mal'ak “messenger, angel.” A deputy commissioned to discharge a certain duty for the principal whom he represents. As the most usual task is that of bearing messages, commands, or tidings, he is commonly called a “messenger” ἄγγελος angelos). The word is therefore a term of office, and does not further distinguish the office-bearer than as an intelligent being. Hence, a מלאך mal'ak may be a man deputed by a man Genesis 32:3; Job 1:14, or by God Haggai 1:13; Malachi 3:1, or a superhuman being delegated in this case only by God. The English term “angel” is now especially appropriated to the latter…”

“16:4-6 Perhaps Hagar expected to become the favored wife instead of Sarai (cp. Prov 30:21-23).”