The Labyrinth is remembered as a story about a monster in a maze. I think it's actually a story about promises, and the monster and the maze are what happens when people don't keep them. There are two promises in it, one at the start and one at the end, and both are broken by careless men. Everything else, the tribute, the thread, the abandoned princess, the crown in the sky, is the fallout.
The bull that wasn't sacrificed
Start at the beginning, which is not with Theseus. It is with Minos, the king of Crete, who wanted to prove that the gods favoured his claim to the throne. He prayed to Poseidon to send a bull from the sea, promising to sacrifice it. Poseidon did. It was a magnificent animal. And Minos, enchanted by it, put it in his own herd and sacrificed a different one.
That's the first broken promise, and it's tiny. A swap of one bull for another. But the god notices. In punishment, Poseidon, or in some versions Aphrodite, makes Minos's wife Pasiphae fall in love with the bull. She asks the craftsman Daedalus for help. He builds a wooden cow and she hides inside it. The result is the Minotaur, a man's body with a bull's head, whose name means the bull of Minos.
Minos is ashamed and has Daedalus build a structure to hold the creature. That is the Labyrinth. The name may come from labrys, a Cretan word for the double axe, and the great palace at Knossos, with its mazelike corridors, has often been suggested as the source of the legend. Whether or not that's right, it's a lovely idea: that a real building became a story because it was too complicated to explain.
The debt
Next comes the tribute. Minos's son Androgeos was killed in Athens, by the Athenians according to most versions, and Minos took revenge. He attacked the city and demanded, every nine years in some tellings, every year in others, seven young men and seven young women to be sent to Crete. They were put into the Labyrinth for the Minotaur to eat.
Here the whole city of Athens is paying for someone else's mistake, with the lives of its young. I find that striking. The monster is not the villain of the story. It is the instrument of a debt, one that began with a swapped bull and was passed on through two generations. Everyone in the myth is paying for something they didn't personally do.
The thread
Theseus, prince of Athens, volunteers to go as one of the youths. When he arrives in Crete, Ariadne, Minos's daughter, falls in love with him. She gives him a ball of thread, taught by Daedalus, which he ties at the entrance and unwinds as he goes. He kills the Minotaur, follows the thread back out and escapes with the other Athenians and with Ariadne.
What I like is how the thread works. It's not a weapon. It's a solution to a navigation problem. The Labyrinth was not hard because the Minotaur was strong. It was hard because nobody who went in could find the way back. The thing that defeats it is a ball of string from a woman who understood the building. As a lesson in what counts as heroism, it's wonderfully unglamorous.
The abandonment
On the way home, they stop on the island of Naxos, and Theseus leaves Ariadne there. The reasons vary. In some versions Dionysus appears to him in a dream and claims her. In others he simply forgets, or deserts her. In Homer's Odyssey, Artemis kills her on Dia at Dionysus's word. In the most common later telling, she wakes alone on the shore, and Dionysus finds her, marries her and sets her crown among the stars, where it becomes the constellation Corona Borealis.
It's a strange moment of moral ambiguity. The woman who made the whole victory possible is left behind, and the myth lets a god step in so that she isn't ruined. But the hero's behaviour is never really excused. The Greeks knew a rotten deal when they saw one.
The white sail
Now the second promise. Before Theseus left Athens, he told his father Aegeus that if he succeeded he would change the ship's black sail for a white one on the way home, so that the old king would know he was alive. He forgot. The ship came into sight with its black sail still flying. Aegeus, watching from the cliff, assumed his son was dead and threw himself into the sea. The sea is called the Aegean after him.
That is the second broken promise, and it is as small and as terrible as the first. A bull swapped. A sail not changed. One happens at the start, the other at the end, and they bracket the whole myth like bookends. The hero who kills the monster is undone by a lapse of attention that costs him his father.
A tidier version
One of the nicest oddities is what happened when later writers got uncomfortable with the monster. Plutarch, in his life of Theseus, reports an alternative version in which the Minotaur was not a creature at all but a Cretan general named Taurus, whom Theseus defeated in a contest. The Labyrinth, in that account, was simply a prison. The story stays, but the supernatural is edited out.
I think that tells you how powerful the myth was. People kept trying to make it more reasonable, and kept failing, because the version with the bull-headed man in the maze was the one that stuck.
What I take from it
If I had to say what the Labyrinth is about, I'd say consequences. Every bad thing in it traces back to a small failure to do what was promised, and every attempt to fix it, whether by sacrifice, by cunning or by love, comes with a new debt. The monster is a symptom. The real subject is how a minor betrayal at the top of a family can ripple through two generations and end with a king throwing himself off a cliff. It's a cautionary tale that has nothing to do with strength.