Abraham was the father of Isaac. The sons of Isaac: Esau and Israel.
Israel was the chosen nation, elect in type; no other people in their national capacity held the covenant privilege the Jews held. The Lord knows His own by name, and many good souls outside Abraham's seed surely found favor with Him, but this genealogy traces the one nation incorporated into His peculiar bond. The Ishmaelites get scant notice because they were cast out as children of the bondwoman, and their rejection foreshadowed the unbelieving Jews rejected after.
AI summary
Commenting on 1 Chronicles 1:28-54
1Ch 1:34 The two sons of Isaac. Isaac has been already mentioned as a son of Abram, along with Ishmael, in 1Ch 1:28. But here the continuation of the genealogy of Abraham is prefaced by the remark that Abraham begat Isaac, just as in Gen 25:19, where the begetting of Isaac the son of Abraham is introduced with the same remark.