What does Genesis 21:6 mean?

Previous verses listed the facts of Isaac's birth. God has done as He said. He has kept His promise. The long-awaited child, the one who makes all future promises possible, has at last been born to a 100-year-old man and his childless, 90-year-old wife. This child is a blessing Abraham and Sarah have both desperately wanted for many years.

Here, we are witness to Sarah's joyful emotional response. In a play on words, she gives all the credit for the birth of Isaac to the Lord. He has "made laughter" for her—Isaac's name means "laughter." Everyone who hears her story will laugh over her or with her, or perhaps she means people will laugh "at" her. Most scholars interpret this statement to mean Sarah believes her story will bring the joy of laughter to others. Some suggest that perhaps she believes others will laugh, as she did, at the idea that a 90-year-old woman could bear a child.

In any case, it has happened. She has laughter, at last.