Forty million Frenchmen," said Shaw, attacking some endlessly popular Gallic comedy, "can't be right." But, of course, they can be. And never more so than in their love of Molière, whose Les Fourberies de Scapin (Scapin's Trickery) the Comédie Française have brought to the Barbican theatre. After torture by musical, in the shape of Notre-Dame de Paris and Lautrec, it's good to be reminded of the heights to which French theatre can rise.

But why is Molière a great dramatist? In part, it's because he has the fundamental sanity of genius: the ability to view human beings, for all their follies and fixations, with a calm, Olympian understanding. This is precisely the quality that makes Shakespeare greater than Ben Jonson, Ibsen superior to Strindberg. But Molière also realised, like Shakespeare and Mozart, that comedy must also contain its opposite: that an awareness of pain, transience and even death counterpoints comedy's celebratory urge.

You can see all this in Les Fourberies de Scapin, which Molière wrote in 1671 towards the end of his relatively short life. On one level, you could say it is knockabout farce borrowing the tricks of the Italian commedia. Two young men are in love with girls they fear their fathers will reject. Needing money to help the girls out, they use the servant Scapin to prise the loot out of the skinflint fathers' hands. But, since the two girls turn out to be the respective fathers' daughters, all ends happily; except that Scapin enters, ostensibly on the point of death, seeking forgiveness.

In strict plot terms, Scapin's actions are unnecessary: the misunderstandings would have sorted themselves out anyway. But Molière's play is not about plot, it is about the superior wisdom of servants and the assertion of natural justice. You see this in its most famous scene where Scapin, falsely accused by one of the fathers, persuades the old man to escape his enemies by hiding in a sack. Scapin then thwacks the sack with a stick while playing the dual role of the old man's protector and his pursuing foes.

This scene becomes the comic centrepiece of Jean-Louis Benoit's wondrously cool, alert production. It has the cruelty of farce as the sack, containing the black-and-blue Géronte, goes swinging back and forth across the stage. But it also becomes about crime and punishment and a delight in role-playing. Gérard Giroudon's brilliant Scapin gets so carried away by the mock-drama he is enacting that he starts to flagellate and pinion himself; and, even after Malik Faraoun's Géronte has raised his head out of the sack to tumble the ruse, Giroudon exits swinging his cudgel with unfazed insouciance.

Scapin is one of the great roles of French theatre. Copeau played him as gentle and romantic, Barrault as an exuberant clown. But Giroudon, more intriguingly, makes him a rueful Beckettian philosopher in a battered trilby. His muscular, athletic legs are also belied by his wispy, white locks, which suggest an aged wisdom. This Scapin is a natural solitary who has clearly been bruised by life and who, when he tells us that "it's better to be married than dead", shoots a questioning glance at the audience. What drives him on is a passion for justice. He beats Géronte because his integrity has been traduced; and, when he cons the old dads of their loot, it is as if he is carrying on a private campaign for the redistribution of wealth.

Giroudon and Benoit realise the play is not a farce: it is a philosophic comedy. It is also part of a great theatrical and literary tradition that shows servants as infinitely wiser than their masters. It is there in Shakespeare, Marivaux, Goldoni, Brecht and continues right up to PG Wodehouse: as Penelope Gilliatt once said, "without the appallingly expert European sense of class distinctions, a good half of post-antique comedy would scarcely exist."

But Molière's wise comedy goes even beyond an assertion of the moral and practical wisdom of servants. At the end, as the reunited fathers and children dance off in celebration, a dazed, blood-spattered Scapin is left alone on stage reminding us that, while his assumed death may be a ruse, mortality is an inescapable fact. As in all great comedy, we are caught between laughter and tears.

Sadly, on the first night there was a far-from-full house to share the experience. There are only a handful of opportunities left to catch Giroudon's performance and Benoit's staging of a play that proves why Molière, even when writing in prose, was a consummate theatrical poet.

• At the Barbican, London EC2 (020-7638 8891), till Wednesday.