Genesis 18:1, 10-14
1 And the Lord appeared unto him in the plains of Mamre: and he sat in the tent door in the heat of the day;
10 And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him.
11 Now Abraham and Sarah were old and well stricken in age; and it ceased to be with Sarah after the manner of women.
12 Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also?
13 And the Lord said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old?
14 Is any thing too hard for the Lord? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son.
-We are told previously in scripture that Sarah was barren even in her youth (Genesis 11:30); she is now past the point when even a normal woman would be able to conceive a child and yet the Lord promises that at nearly 100 years old, she will do exactly that. The sheer size of the Lord’s promise leads her to question it; “If I couldn’t have a child all of these years, how am I supposed to have one now that I’m old?” The Lord reminded Abraham and Sarah that there is really only one question, “Is anything too hard for the Lord?” Focusing on our circumstances will inevitably lead to doubt because our circumstances can get very big. But if we focus on God instead, we will be able to see how much bigger He is and that “with [Him] all things are possible.” (Matthew 19:26)