John Gill Commentary Genesis 21:3

"And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac." — Genesis 21:3 (ASV)

And Abraham called the name of his son that was born to
him, whom Sarah bore to him, Isaac .
] This is the name he was directed to give him, (Genesis 17:19) ; and he remembers the order, and is obedient to it; the reason of which name, which signifies laughter, was because of his laughing for joy at the promise made him, and there might be afterward a further reason for it, from Sarah's laughing because of distrust; and it might presignify the joy and laughter that would be expressed by others at his birth; and perhaps that he would be the object of the laughter and derision of his brother; so many events agreeing with his name.