In Chapter 1 of Tuck Everlasting, we read that the Wood is the hub [of the wheel of life]. In this comment, Winnie is acknowledging the fact that Nature is of utmost importance in the book Tuck Everlasting.  In Tuck, Nature is an important Theme.

Nature as a Theme in Literature

When Nature is a literary theme, the writer is usually talking about more than the flora of an area. The writer is usually talking about an idealized natural world that predated technology and industrialization. By the time that the action of Tuck Everlasting takes place, civilization has already encroached on one side of the wood, and the state of idealized harmony there has been disrupted:

“On the other side of the wood, the sense of easiness dissolved. The road no longer belonged to the cows. It became, instead, and rather abruptly, the property of people. And all at once the sun was uncomfortably hot, the dust oppressive, and the meager grass along its edges somewhat ragged and forlorn. On the left stood the first house, a square and solid cottage with a touch-me-not appearance, surrounded by grass cut painfully to the quick and enclosed by a capable iron fence some four feet high which clearly said, “Move on—we don’t want you here.”

As houses and villages and businesses and factories are built, the natural world is compromised. In Tuck Everlasting, Winnie Foster lives in one of the houses in Treegap. In other words, Winnie’s feet are planted in the more industrialized and less ideal part of the area in and around Treegap. In Tuck Everlasting, Winnie is the girl who falls in love with Jesse Tuck. Jesse’s feet are planted in the primordial, unadulterated, natural Wood.\ Winnie says that at one time, the entire area was a forest [or Wood.

 “…this was all trees once, just one big forest everywhere around, but it’s mostly all cut down now. Except for the wood.”

Therein lies one of the conflicts in the book Tuck Everlasting. Idyllic, un adulterated Nature is being replaced by modernization.

In Chapter 4, a curious man in a yellow suit appears:

4
“At sunset of that same long day, a stranger came strolling up the road from the village and paused at the Fosters’ gate. Winnie was once again in the yard, this time intent on catching fireflies, and at first she didn’t notice him. But, after a few moments of watching her, he called out, “Good evening!”
He was remarkably tall and narrow, this stranger standing there. His long chin faded off into a thin, apologetic beard, but his suit was a jaunty yellow that seemed to glow a little in the fading light. A black hat dangled from one hand, and as Winnie came toward him, he passed the other through his dry, gray hair, settling it smoothly. “Well, now,” he said in a light voice. “Out for fireflies, are you?”

In terms of Night and Day [Darness and Light] as themes, Sunset is approaching the time of Darkness. The man in the yellow suit appears in the story near nightfall. Through use of the time of day that he appeared, Babbitt is giving us a clue about his character.

Dark versus Light – Night versus Day – Themes in Literature

{In my opinion, the fact that Winnie is searching for fireflies is evidence that she is seeking some enlightenment–some tonic for the hazards of the darkness of the night].

The man in the yellow suit pauses at Winnie’s gate.

Reference to the gate [and thus, the fence] offers us another hint:

A Fence by Carl Sandburg

It is significant that the man in the yellow suit stands on the other side of the  Fosters’ Fence. Winnie’s grandmother comes down to see who is at the gate, and the man in the yellow suit asks the grandmother if she knows everyone in the area. The grandmother responds:

“I don’t know everyone,” she said, “nor do I want to. And I don’t stand outside in the dark discussing such a thing with strangers. Neither does Winifred. So . . .”
And then she paused. For, through the twilight sounds of crickets and sighing trees, a faint, surprising wisp of music came floating to them, and all three turned toward it, toward the wood. It was a tinkling little melody, and in a few moments it stopped.
“My stars!” said Winnie’s grandmother, her eyes round. “I do believe it’s come again, after all these years!”
She pressed her wrinkled hands together, forgetting the man in the yellow suit. “Did you hear that, Winifred?
That’s it! That’s the elf music I told you about. Why, it’s been ages since I heard it last. And this is the first time you’ve ever heard it, isn’t it? Wait till we tell your father!” And she seized Winnie’s hand and turned to go back into the cottage.
“Wait!” said the man at the gate. He had stiffened, and his voice was eager. “You’ve heard that music before, you say?”
But, before he could get an answer, it began again and they all stopped to listen. This time it tinkled its way faintly through the little melody three times before it faded.
“It sounds like a music box,” said Winnie when it was over.
“Nonsense. It’s elves!” 

Not only is the writing about the sounds of the night beautiful in the above passage, it suggests that a bit of fairy magic is about to enter the story. The stars and the moon are part of that bit of fairy magix, and Babbitt references both the Stars and the Moon in chapter 4:

.“The last stains of sunset had melted away, and the twilight died, too, as he stood there, though its remnants clung reluctantly to everything that was pale in color—pebbles, the dusty road, the figure of the man himself—turning them blue and blurry. Then the moon rose. The man came to himself and sighed. His expression was one of intense satisfaction. He put on his hat, and in the moonlight his long fingers were graceful and very white. Then he turned and disappeared down the shadowy road, and as he went he whistled, very softly, the tinkling little melody from the wood.”

Babbitt has introduced the stars and the moon as light sources that illuminate the night. The Stars and the Moon are Darkness Busters.

In Chapter 5, we read that WInnie is about to embark upon a journey.

Journeys in Literature

5
“Winnie woke early next morning. The sun was only just opening its own eye on the eastern horizon and the cottage was full of silence. But she realized that sometime during the night she had made up her mind: she would not run away today.]

But

“Well, anyway, she could at least slip out, right now, she decided, and go into the wood. To see if she could discover what had really made the music the night before. That would be something, anyway.”

Winnie set out on her journey into the Woods.

Immediately, Winnie notices that is cooler in the shade, where the trees block the blazing sun. Babbitt’s description of the woods is beautifully written:

“It was another heavy morning, already hot and breathless, but in the wood the air was cooler and smelled agreeably damp. Winnie had been no more than two slow minutes walking timidly under the interlacing branches when she wondered why she had never come here before. “Why, it’s nice!” she thought with great
surprise. For the wood was full of light, entirely different from the light she was used to. It was green and amber and alive, quivering in splotches on the padded ground, fanning into sturdy stripes between the tree trunks. There were little flowers she did not recognize, white and palest blue; and endless, tangled vines; and here and there a fallen log, half-rotted but soft with patches of sweet green-velvet moss. And there were creatures everywhere. The air fairly hummed with their daybreak activity: beetles and birds and squirrels and ants, and countless other things unseen, all gentle and self-absorbed and not in the least
alarming. ” …

“There was a clearing directly in front of her, at the center of which an enormous tree thrust up, its thick roots rumpling the ground ten feet around in every direction. Sitting relaxed with his back against the trunk was a boy, almost a man. And he seemed so glorious to Winnie that she lost her heart at once.
He was thin and sunburned, this wonderful boy, with a thick mop of curly brown hair, and he wore his battered trousers and loose, grubby shirt with as much self-assurance as if they were silk and satin. A pair of green suspenders, more decorative than useful, gave the finishing touch, for he was shoeless and there was a twig tucked between the toes of one foot. He waved the twig idly as he sat there, his face turned up to gaze at the branches far above him. The golden morning light seemed to glow all around him, while brighter patches fell, now on his lean, brown hands, now on his hair and face, as the leaves stirred over his head. Then he rubbed an ear carelessly, yawned, and stretched. Shifting his position, he turned his attention to a ittle pile of pebbles next to him. As Winnie watched, scarcely breathing, he moved the pile carefully to one side, pebble by pebble. Beneath the pile, the ground was shiny wet. The boy lifted a final stone and Winnie saw a low spurt of water, arching up and returning, like a fountain, into the ground. He bent and put his lips to the spurt, drinking noiselessly and then he sat up again and drew his shirt sleeve across his mouth. As he did this, he turned his face in her direction—and their eyes met.”