Hebrews 11:
No, at this point, God had not explicitly told them that she would bear a son. That came in the next chapter. Gen 17:
God visited Abraham in the next chapter, 18:
Genesis 21:
No one had perfect faith, not Abraham, not Sarah. In the end, God is gracious to focus on the positives and ignores Sarah's one-time laughter of disbelief. By the time of the OT Hebrews 11:
Really? Was Sarah faithful?11 By faith Sarah herself received power to conceive,
God promised Abram descendants in Genesis 15:even when she was past the age, since she considered him faithful who had promised.
Sarai couldn't wait. Genesis 16:18 On that day the LORD made a covenant with Abram and said, “To your descendants I give this land, from the Wadi of Egypt to the great river, the Euphrates."
Was Sarai being unfaithful to God's promise?1 Now Sarai, Abram’s wife, had borne him no children. She had a female Egyptian servant whose name was Hagar. 2 And Sarai said to Abram, “Behold now, the LORD has prevented me from bearing children. Go in to my servant; it may be that I shall obtain children by her.”
No, at this point, God had not explicitly told them that she would bear a son. That came in the next chapter. Gen 17:
At this news, Abraham laughed but not in a mocking way. He thought it was funny.15 And God said to Abraham, “As for Sarai your wife, you shall not call her name Sarai, but Sarah shall be her name. 16 I will bless her, and moreover, I will give you a son by her. I will bless her, and she shall become nations; kings of peoples shall come from her.” 17 Then Abraham fell on his face and laughed and said to himself, “Shall a child be born to a man who is a hundred years old? Shall Sarah, who is ninety years old, bear a child?”
God visited Abraham in the next chapter, 18:
Sarah did not laugh at God. It was a one-time reaction of surprise and disbelief. She still believed in God.9 They [the LORD] said to him, “Where is Sarah your wife?” And he said, “She is in the tent.” 10 The LORD said, “I will surely return to you about this time next year, and Sarah your wife shall have a son.” And Sarah was listening at the tent door behind him. 11 Now Abraham and Sarah were old, advanced in years. The way of women had ceased to be with Sarah. 12 So Sarah laughed to herself, saying, “After I am worn out, and my lord is old, shall I have pleasure?”
Sarah feared the LORD because her laughing was detected. She knew she should not have laughed. She knew she should have taken the word of the LORD seriously. She regretted. Sarah's reactions were human and understandable.13 The LORD said to Abraham, “Why did Sarah laugh and say, ‘Shall I indeed bear a child, now that I am old?’ 14 Is anything too hard for the LORD? At the appointed time I will return to you, about this time next year, and Sarah shall have a son.” 15 But Sarah denied it, saying, “I did not laugh,” for she was afraid. He said, “No, but you did laugh.”
Genesis 21:
God's promise was fulfilled in Sarah.1 Now the LORD attended to Sarah as He had said, and the LORD did for Sarah what He had promised. 2 So Sarah conceived and bore a son to Abraham in his old age, at the very time God had promised.
These were laughter of joy. Sarah believed.6Then Sarah said, “God has made me laugh, and everyone who hears of this will laugh with me.” 7 She added, “Who would have told Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.”
in a mocking way.8 And the child grew and was weaned. And Abraham made a great feast on the day that Isaac was weaned. 9 But Sarah saw the son of Hagar the Egyptian, whom she had borne to Abraham, laughing
That's a word of faith from Sarah.10 So she said to Abraham, “Cast out this slave woman with her son, for the son of this slave woman shall not be heir with my son Isaac.”
God agreed with Sarah; rather, Sarah agreed with God.11 And the thing was very displeasing to Abraham on account of his son. 12 But God said to Abraham, “Be not displeased because of the boy and because of your slave woman. Whatever Sarah says to you, do as she tells you, for through Isaac shall your offspring be named.
No one had perfect faith, not Abraham, not Sarah. In the end, God is gracious to focus on the positives and ignores Sarah's one-time laughter of disbelief. By the time of the OT Hebrews 11:
The blood of Christ covers our negatives. That's good news. Three chapters earlier, Hebrews 8:11 By faith Sarah herself received power to conceive, even when she was past the age, since she considered him faithful who had promised.
Because of the Cross, God ignores Sarah's one-time reaction of disbelief.12 For I will forgive their wickedness and will remember their sins no more.”