Genesis 17:21
“But my covenant will I establish with Isaac, which Sarah shall bear unto thee at this set time in the next year.”
KJV
Read in Genesis 17Meaning
God identifies Isaac as the covenant line and says Sarah will bear him at the appointed time in the following year.
Read carefully
The covenant distinction should be read within Genesis and not converted into hostility toward Ishmael's descendants or a one-verse modern political mandate.
Reflection
The promise receives both a name and a timetable, narrowing the narrative expectation from a general hope of descendants to the birth of Isaac.