Genesis 21 · a question people ask
What was Ishmael doing when Sarah saw him?
The WEB says Sarah saw him "mocking" (21:9). The Hebrew is a form of tsachaq, the verb for laugh in 21:6; in this form Brown-Driver-Briggs glosses it "jest" and "sport, play". Genesis doesn't say more about what he did. Protestants read it in two main ways.
How Christians read it
Where Christians differ, Favor sets out the main views side by side and doesn't pick one.
He was mocking Isaac
Those who hold this view point to Paul, who writes of this episode, "as then, he who was born according to the flesh persecuted him who was born according to the Spirit" (Galatians 4:29). The WEB translates the same form of the verb "mock" in 39:14, "to mock us".
Galatians 4:29 · Genesis 39:14
He was laughing or playing
Those who hold this view point to the verb's range in Genesis: laughing (17:17; 21:6), joking (19:14) and caressing (26:8). They note that Sarah's stated reason is the inheritance: "the son of this servant will not be heir with my son, Isaac" (21:10).
Genesis 17:17 · Genesis 19:14 · Genesis 26:8 · Genesis 21:10
The verses
“Sarah said, “God has made me laugh. Everyone who hears will laugh with me.””
“Sarah saw the son of Hagar the Egyptian, whom she had borne to Abraham, mocking.”