en_tn_condensed/heb/11/12.md

descendants as many as the stars in the sky and as countless as sand by the seashore

This simile means Abraham had very many descendants. (See: rc://en/ta/man/translate/figs-simile)

as countless as sand by the seashore

This means that just as there are so many grains of sand on the seashore that no one can count them all, Abraham had so many descendants that no one can count them all.