Genesis 21

1 Sarah was already past menopause. Therefore, it took a direct and miraculous intervention from God to help her conceive.
3 There had been laughter of wonder and incredulity when Isaac's birth was predicted. Isaac's birth brought joy and laughter back into Sarah's life. Therefore Isaac (derived from the word "to laugh") was the perfect name for him.
4 In accordance with Gen 17:12.
7 God had done the impossible.