“Seed”

Here is Robert Alter, introducing The Hebrew Bible: A Translation with Commentary.

When … God reiterates his promise to Abraham, the multiplication of seed is strongly linked with cosmic imagery – harking back to the creation story – of heaven and earth: “I will greatly bless you and greatly multiply your seed, as the stars in the heavens and as the sand on the shore of the sea” (Genesis 22:17). If “seed” here is rendered as “offspring” or “descendants,”

– as in recent translations (but not the King James Version) –

what we get are two essentially mathematical similes of numerical increase. That is, in fact, the primary burden of the language God addresses to Abraham, but as figurative language it also imposes itself visually on the retina of the imagination, and so underlying the idea of a single late-born son whose progeny will be countless millions is an image of human seed (perhaps reinforced by the shared white color of semen and stars) scattered across the vast expanses of the starry skies and through the innumerable particles of sand on the shore of the sea. To substitute “offspring” for “seed” here may not fundamentally alter the meaning but it diminishes the vividness of the statement, making it just a little harder for readers to sense why these ancient texts have been so compelling down through the ages.