Genesis 18: 13-14
13 Then the LORD said to Abraham, “Why did Sarah laugh and say, ‘Will I really have a child, now that I am old?’ 14 Is anything too hard for the LORD? I will return to you at the appointed time next year, and Sarah will have a son.”
That Sarah laughed at god because she didnt believe that she could have a child when she was already really old. She didn't believe that god would give her a child at her age.
That even if it seems silly, he has a plan for us. And we should not mock him by laughing at his plan for us.
To make me more like god.