Essay zu Bereschit 21:39

Two principal ideas punctuate this climax for which we have waited since Chap. 12: God keeps his promises (hence the poem in v.1), and the key word in the stories about Yitzhak: “laughter” (here the result of the actual birth).

This interlude, which usefully separates the life threats to Avraham’s two sons (for a similar example, see I Sam. 25), is one of many scenes demonstrating Avraham’s relationship with local princes.