John Calvin on Genesis 21:18-19

18. Arise lift up the lad . In order that she might have more courage to bring up her son, God confirms to her what he had before often promised to Abraham. Indeed, nature itself prescribes to mothers what they owe to their children; but, as I have lately hinted, all the natural feelings of Hagar would have been destroyed, unless God had revived her, by inspiring new confidence, to address herself with fresh vigor to the fulfillment of her maternal office. With respect to the fountain or “well,” Ver. 19. “God opened her eyes, and she saw a well of water.” “Quod ad fontem pertinet,” are Calvin’s words; but in his version it stands, “puteum aquae,” a well of water. — Ed some think it suddenly sprung up. But since Moses says, that the eyes of Hagar were opened, and not that the earth was opened or dug up; I rather incline to the opinion, that, having been previously astonished with grief, she did not discern what was plainly before her eyes; but now, at length, after God has restored her vision, she begins to see it. And it is worthy of especial notice, that when God leaves us destitute of his superintendence, and takes away his grace from us, we are as much deprived of all the aids which are close at hand, as if they were removed to the greatest distance. Therefore we must ask, not only that he would bestow upon us such things as will be useful to us, but that he will also impart prudence to enable us to use them; otherwise, it will be our lot to faint, with closed eyes, in the midst of fountains.