Therefore Sarah laughed within herself, saying, “After I have grown old, shall I have pleasure, my lord being old also?” And the Lord said to Abraham, “Why did Sarah laugh, saying, ‘Shall I surely bear a child, since I am old?’ Is anything too hard for the Lord? At the appointed time I will return to you, according to the time of life, and Sarah shall have a son.” But Sarah denied it, saying, “I did not laugh,” for she was afraid. (Gen 18,12-15)

Sarah certainly considered herself a worshipper of the Lord, for she had no other gods. She was, after all, a member of the only community at that time whose faith was based on the direct revelation God gave to their leader Abraham. After all - consider - God spoke to him from mouth to mouth! So Sarah was in the position of a member of the congregation, in effect, the "pastor's wife." But how close a person can be to God's dealings, or to another person with whom God has dealt, and yet be little affected himself...

Sarah, unlike Abraham, has so far known religion more in its external forms. She resembles religious people from ancient times to the present day. While the worst sins disappear from life, measured externally such a person is better than most people. Yet he lacks the faith that would carry him to a higher sphere, lacks the supernatural experience that leads to inner transformation, and therefore cannot stand the light before God. The first recorded manifestation of Sarah's attitude (where she acts of her own volition, not just following her husband's faith) is the universal pervasive fear of "what will happen to us" - if God fails. So she devises a way to bypass God and get the baby. (You can have faith, but in the end, what's left?) And later: she hides from God's messengers in a tent because she doesn't want to and can't be an open book in front of them - she hasn't given her true self to God yet. As a result, she cannot move beyond the flesh and see with spiritual sight, so she laughs at the miracle God has come to announce. Secretly, of course, lest God should happen to notice!

The religious person likes to point out what he is better at than other people (Luke 18:11). Of course, he picks out the areas where he really is and makes sure of it. But he misses the fact that God wanted a change of heart in the first place. Centuries later, therefore, Jesus said to the devout Pharisees, "tax collectors and harlots enter the kingdom of God before you." (Matt. 21:31) And a little further on,  “Woe to you, scribes and Pharisees, hypocrites! For you pay tithe of mint and anise and cummin, and have neglected the weightier matters of the law: justice and mercy and faith. These you ought to have done, without leaving the others undone." (Mt 23:23)

God was really angry that Sarah, after 25 years of following, was laughing at the hope He was announcing to them. There is perhaps no other instance in all of Scripture where God silenced someone like this ("but yes, you laughed"). It demonstrates how God immediately perceives and responds to the faith or, conversely, unbelief in a person's heart.