קבלה אויף בראשית 25:12

We derive also another lesson from this verse. It is written “And these are the generations of Isaac” (Gen. 25, 19), and a few verses before (Ibid. 12) the text says, “And these are the generations of Ishmael”, and goes on to enumerate twelve princes. Seeing that Isaac had only two sons, we might think that in this respect Ishmael was superior to him. But in truth it is just in allusion to Isaac that Scripture exclaims: “Who can express the mighty acts of the Lord?” the term “mighty acts” being an allusion to Isaac. For Isaac begat Jacob, who in his own self excelled them all, and who further begat twelve tribes, through whom all both above and below were firmly established. Isaac was invested with the sanctity of the supernal world, whereas Ishmael was of the lower world. Hence it says: “Who can express the mighty acts of the Lord, or make the whole of his praise to be heard?” the latter clause alluding to Jacob, as much as to say: “When the sun joins the moon innumerable stars are thereby illumined.”