There is actually a field of study devoted to laughter: Gelotology.

Scientists say we laugh when reality suddenly changes, disrupted by something strange. What we expected to happen does not happen. Our minds trip for a second. Then, realizing nothing fell apart when the unexpected happened, the physical expression of laughter resets us.

Maybe that is why Sarah laughs. Because God interrupts everything she thought would happen with a strangely, absurdly comforting encounter.

This story may end in laughter and the naming of Isaac, child of laughter, but its beginning is no laughing matter.

Before this story is a comedy, it is a tragedy. And it's a tragedy we need to pay attention to.

Scholars situate this story in what they call "The Ancestors," the thematic material of the Hebrew Bible. These stories highlight "elemental themes of faith" for each generation to learn and retell.

For generations, communities told and retold the tragic story of Abraham and Sarah, who tried for seven-plus decades to have a family, only to at last have their dream come true in the most absurd way.

Y'all, let me reiterate. Sarah is 90 years of age.

Do you know what it's like to be 90?

I've lived with my grandmother for a period of time while she was in her 80s. I see her when I see Sarah, bent by time and the tasks of keeping a household, steps uneven and unsteady.

No lidocaine patch for Abraham to place on Sarah's back before bed. Life, a cycle of sweeping, mending, power naps, cooking, cleaning, in Canaan, where Abraham decided to set up camp within view of a mountain called barren.

Yet another comedic and tragic layer to this story.

But something seems to be shifting in this tragic chapter of the couple's life. Lately, there has been a lot of God-talk about children, though Sarah is not getting any of this information directly from the source. Abraham is telling Sarah of these encounters with God and promises of a lineage of children so grand, more than the stars in the sky, more than the grains of sand beneath their feet, that Sarah is beginning to wonder if her partner has, at 99 years of age, finally started to lose his mind.

At what age did Sarah resign herself to barrenness?

At 20, still hopeful, she and Abraham are dreaming dreams and making a list of names.

At 30, some hope, but a little bit of anxiety now palpable between the couple as they lie in bed, crushing disappointment every 28 days.

At 40, cynicism and now scheming, a backup plan. More palpable silence between them.

50, 60, 70, 80, 90. Barren.

All signs point to the logical conclusion that it is too late to rewrite the story.

Why did Sarah laugh?

I again see my grandma's face being told in one of her regular visits to the doctor that in the next year she will give birth to a child. Surely she and we would not be able to hold back our reaction. A laugh, a guffaw. If I'm sipping tea, probably a spit-take. A natural response to something so preposterous, so absurd that you're not sure whether to cry, scream, or, as Sarah does, laugh.

Frederick Buechner asks of this story, "Where does Sarah's laughter come from? It comes from as deep a place as tears come from, and in a way, it comes from the same place. As much as tears do. It comes out of the world where God is seemingly absent."

Preaching a sermon like this to a camera, not knowing exactly who you are and what feels impossibly barren and tragic for you, is a unique challenge. Yet I think some of you are struggling to navigate life in a world where God is seemingly absent.

We are feeling barren and crushingly alone in this barrenness.

Does God hear our cries? Or is God absent?

There is a clue in the verses that follow Sarah's laughter, which God makes clear is heard.

In between the readings from Genesis this Sunday is a tragic story that many have struggled to make sense of.

You see, after these strangers visit Abraham and Sarah, they continue their journey and arrive at Sodom, taking Abraham with them. And God speaks to Abraham, being honest about the Divine's feelings of sorrow over a seemingly thriving city that on the inside is barren of life.

"Abraham," says God, "the outcry I've heard against Sodom and Gomorrah is terrible. I had to come see for myself."

One scholar notes that the outcry God hears is actually the cry of a particular woman in Sodom who was put to death because she had given food to a poor person.

Abraham and Sarah welcomed these strangers to their home. Sodom rejects them.

One story opens towards life from absurdity: comedy. And the other collapses in on itself absurdly: tragedy.

Jewish tradition interprets this juxtaposition by saying, some civilizations are so cruel to strangers that they bring out their own demise. Evil societies, according to rabbinic tradition, destroy themselves.

But what about those of us who are sick and tired of the demise and the destruction, who desire new life, who don't want to grow hard-hearted and cynical in the barrenness of our days, who see all too clearly the breach between what God says ought to be and what is?

To all of you, I say, we can rewrite the story by drawing near to the strange and to strangers. For in so doing, God is present in disguise.

This is the theme of this section of ancestor tales. It is also a theme throughout the Bible, including the New Testament.

Like the story of Sarah, Abraham and Isaac, the gospel is tragedy first, comedy later.

By comedy, I don't mean that suffering is funny. I mean that God refuses to let death and barrenness have the final word and sees beyond our limited apparent reality.

The gospel story is that a man who seemed very, very much dead, tragedy, exited his tomb on the third day and greeted the women and men he loved in unexpected ways, most of whom could not recognize him at first. Because to see Jesus walking away from a state execution, let alone not one, not two, but three days in a tomb, is absurd comedy.

See Jesus winking as he is mistaken for a gardener in the cemetery.

See him again, smirking as he is mistaken for a stranger on the road to Emmaus.

See him holding back a laugh as his best friends yell, "Ghost!" when he enters the same locked room he sat and shared a meal with them in a few days before.

Absurdly, surprisingly, God comes near and pierces cynical hearts, unlocks doors to rooms where we are trapped by fear, and brings laughter from tears.

And that is what I think this story, embedded in the literature of "The Ancestors," teaches us: that, in fact, the way out of loneliness and hopelessness of our society is to keep an eye out for strangers, to run to them and offer them rest, to swap stories with them, to break bread with them and laugh with them. Because if we ignore those strangers, we ignore God in our midst, offering a wink and revealing to us a way into the greening and unfurling of tender shoots from once dry, cracked land.

Skepticism may linger in these absurdly tragic times, but the laughter shared with strangers will shift something in our perspective. It will resettle us.

And according to Dr. Lee Burk, who studies laughter, laughter quite literally heals us, lowering cortisol, strengthening our immune systems. Laughter is also evidence of comfort and connection. We are more likely to belly laugh in the midst of those we love and trust.

Why does Sarah laugh?

I think Sarah laughs because in the presence of God disguised as these three strangers, the story she thought was settled forever is interrupted. Sarah laughs because she feels safe in the divine presence to respond authentically to the absurdity of God with her own joke, "I was not laughing. You were, God."

Sarah could cry, but she laughs because she knows that the apparent reality of the world no longer holds sway. She senses that the absurdity of being a geriatric mother is more real than the tragedy of being childless. She laughs because the ones who called her barren will now behold with their own eyes the absurdity of God's ways. The one who has the power to make two nonagenarians first-time parents.

And if that is possible, what else is possible with God?

We follow the one whose words and actions often came off as a joke to the powerful, who took themselves too seriously to laugh with God at their meager plans to control the world.

God is a cosmic comedian, giggling as they overturn the scripts we think are final.

Some of you have accepted tragic scripts for your own story or our story as a nation, as a world. And Sarah did too.

But then God arrived as a stranger, having a rest and a meal beneath the trees with good news to share.

And Sarah laughed.

Because when God shows up, stories we thought were settled forever are not settled after all.