When Sarah gives birth to her son, she names him “Isaac” (יצחק; Yitzhaq), saying,
“God has made laughter (צחק; tzhoq) for me; everyone who hears will laugh (יצחק; yitzhaq) with me” (Genesis 21:6).
On the day that Isaac is weaned, Abraham gives a celebratory feast at which
“Sarah saw [Ishmael] the son of Hagar the Egyptian, whom she had borne to Abraham, laughing.”
When Ishmael is seen “laughing” (מצחק) at the feast, his action recalls the name “Isaac,” which means “he laughs” (יצחק).
These related Hebrew words point to the notion that Ishmael was not merely “laughing”; rather, he was “Issac-ing”! That is, he was behaving as though he were Isaac, the rightful heir of God’s promise.
The idea that Ishmael was “trying to be like Isaac” makes more sense of Sarah’s words to Abraham:
“Cast out this slave woman with her son, for the son of this slave woman shall not be heir with my son Isaac” (Genesis 21:10).
Dutch version / Nederlandse versie: Ismaël “lachte” niet enkel maar was “Issaking”