New Defender's Study Bible Notes
21:11 very grievous. Sarah’s insistence that Hagar and Ishmael be cast out was very grievous to Abraham, not only because of his personal concern for them, but because it was expected of a man in those days (according to the Nuzi tablets) to provide support for a surrogate wife and her children, even if the true wife should later be able to have a child of her own. The latter would legally be the heir, but the former would still be considered in the family.
21:14 bottle of water. This provision, considering his sincere concern for Hagar and Ishmael, can best be understood as a sure confidence that God, who had instructed him to send them away, would care for them. Hagar also needed to learn this.
21:17 the lad. Ishmael, who was now about sixteen years old, and his mother were praying. He perhaps had given her his own bread and water to sustain her in the desert.
21:17 angel of God. The “angel of God [Elohim]” had before been called the “angel of the LORD [Jehovah]” (Genesis 16:7). Previously, Hagar was under the Abrahamic covenant while still in Abraham’s household. Now she was on her own and the divine being is identified by His majestic name instead of His redemptive name.