A MAN I KNOW always explains Easter to his children. "Easter," he says solemnly, "is a commemoration of the resurrection of Christ." He describes Christ's torture, tells of his entombment in a cave, and relates the astonishemnt of the people when the great stone is rolled back from the door of the cave to reveal its emptiness. But because my friend is a thorough and honest man, he adds: "And then there is this rabbit that lays chocolate eggs . . . "

I was reminded of this when I read of the Jewish teacher's aide who tossed the school Christmas tree into a parking lot to protest the celebration of the birth of Christ in public schools, and of the Christian teacher who protested the observance of Halloween in schools because it is a pagan custom used to apotheosize evil.

Of course, Christmas trees have no more to do with the birth of Christ than egg-laying rabbits with the Resurrection or trick-and-treat and funny masks with dead souls. All are indeed pagan customs, and, in truth, the pagans knew how to stage religious festivals better than Christians, Jews or Hare Krishnas.

Those ancient rites strike primitive chords in all of us; they are more fun; they take away the solemnity, which few of us are capable of sustaining, and replace it with gaiety. Somehow, priests, pastors, rabbis, gurus and ayatollahs have never had the imagination or the insight or the sense of theater of those ancient pagans who used pine trees, rabbits, masks and other familiar props so effectively. (Let he or she who has never cast rice at newlyweds in a churchyard contrive the first sneer.)

We have not, of course, taken over pagan customs lock, stock and mistletoe. All have undergone a sea change with shifts in geography and the passing of eras. Valentine's Day commemorates an obscure saint about whom almost nothing is known. St. Valentine may have been a misogynist and a misogamist, but he has become by popular acclaim a pagan god of love. Before any anti-saint cult organizes a valentine-card-burning media event in a high school auditorium, let me provide what State Department buffs call a backgrounder.

Once upon a time, before there were Christians or saints, the Romans celebrated Lupercalia as a religious festival. Although the Greek probably had the same or similar festivities earlier, it was the Romans who perfected it, and, it must admitted, no one can surpass the Romans at staging dramatic events. The Roman Lupercalia involved the sacrifice of goats and a dog. Young men, clad in goat skins, smeared themselves with the blood of the unfortunate beasts and then dashed about brandishing goat thongs. All was done in the cause of fertility. As the young men raced around the Palatine, virgins (some naked, it is said) deliberately placed themselves in their path in order to get a cut or two from the goat thongs -- to help them conceive.

Lupercalia was, naturally, a popular festival -- for who would not endure a bit of S & M for a good cause and a religious one too. So popular was it that it endured well into the Christian era and was not suppressed until A.D. 494. It was then replaced by Saint Valentine's Day. So now the pleasure of young men in beating naked girls and the pleasure of the girls in getting thwacked by bloody young men has been replaced by the quieter pleasure of exchanging valentine cards. In a way the ceremony has come full circle, for many a valentine card has proven the first step toward the making of a fertile woman pregnant.