Parsha Vayeira - Chapter 21 – Verses 13 - 14
Hashem is comforting Avraham, don’t worry, Yishmael too is your son and he too will become a great nation.
Yitzhak possessed the middot of gevurah to serve Hashem in all circumstances in all situations. Yitzhak could stand up to the evil inclination. Yitzhak needed to be strong, and whole in order to pass that strength onto us. Because without it the Jewish nation could not survive in this long and bitter exile. It was too dangerous to risk having Yishmael around who could have been a negative influence on Yitzhak and may harm him or kill him. We know he was already jealous from his birth of Yitzhak.
Avraham sends them off with bread and water.