In Genesis 21:14, Abraham sends Hagar and Ishmael away into the desert. Yet Abraham was not sending them to die of thirst there. He gave them a skin of water (21:14); vegetation could grow in that region, and it was habitable (21:30-33; 22:19; 26:23, 33). Unfortunately, Hagar and Ishmael apparently got lost before finding water or any habitation and so ran out of water (21:14-16).
Nevertheless, Abraham had God’s promise concerning Ishmael (17:20), including at this time (21:13), and so could trust God for Ishmael as he could trust God for Isaac when offering him on Mount Moriah in the next chapter. And sure enough, the angel of the Lord again appeared to Hagar, reaffirmed the promise, and pointed her to nearby water (21:17-19). God heard Ishmael’s cries (21:17).
People often blame their own cruel choices on God. That issue merits discussion in its own right, but it is not a discussion of the message of this passage. This passage instead celebrates Abraham’s continued faith and obedience. He knew God’s voice and had witnessed God act miraculously with Sarah’s pregnancy and Isaac’s subsequent birth. This is another step of obedient faith that brought him closer to being ready to sacrifice what will then be his only son, trusting God’s faithfulness no matter what.