A Montaigne to take to heart; Montaigne: A Biography, by Donald M. Frame. San Francisco: North Point Press. 408 pp.$15 (paperback).

Here's a book that satisfies, in these curiously twilit hours, our need for a book in harmony with a summer's evening. The life and books of Michel Eyquem de Montaigne, a 16th-century Frenchman whose ancestral chateau is visited every summer by many who love his ''Essays,'' were so intertwined that his biography is really a study of his writings.

Donald Frame, who has translated the complete ''Essays'' and Montaigne's ''Travel Journal'' (also from North Point), knows his subject so well that this biography presents, for the English reader's purposes, the Montaigne one can take to heart.

One of the two most important events in Montaigne's early life was the first time his tutor, a German doctor chosen by his father, spoke with him in Latin (a game which the household, including mother and father, joined in until he was 6 ).

The other was his meeting, while a counselor in the Bordeaux Parliament, with Etienne de la Boetie, whose Stoic virtue and deep affection left Montaigne permanently in his debt.When la Boetie died four years later, Montaigne's adult life began. Frame conjectures persuasively - and here the strengths of his exposition shine - that the loss of this friendship ripened into Montaigne's mature art of self-discovery on the written page. Of his friend, Montaigne later wrote: ''He alone enjoyed my true image, and carried it away. That is why I myself decipher myself so painstakingly.''

Latin was virtually Montaigne's native language. And the ''Essays'' are the fruits of his lifelong study of the Latin books that stocked his memory and library. Frame is an accurate guide to Montaigne's quarrel with Stoicism: There was a human perfectionism about Stoicism that Montaigne increasingly distrusted (as did Horace, whose late poems one can't read without thinking of Montaigne's ''Essays'').

When one reads Montaigne, one reads oneself. We are all riddles, and an essay by Montaigne is an attempt (the word essay comes from the verb essayer, to try) to get a fix on some aspect of man's constantly changing sense of identity.

Readers of Frame will be kept from the mistake of thinking Montaigne a skeptic: The essayist's introspection was performed under the aegis of his faith. Montaigne, too often considered a humanist in the modern sense, ably defended the religious center in a time of fanaticism - this center being faith itself.

Montaigne's universal appeal comes not from his attack on dogmatism only, but from the faith-grounded freedom and confidence he experienced and communicates to his readers.

As for his skepticism, Montaigne writes: ''God must touch our hearts. Our conscience must reform by itself through the strengthening of our reason, not through the weakening of our appetites.''

At points in this book one forgets where text ends and commentary begins. After quoting Montaigne, Frame goes on: ''In public we wear a mask, play a part, display our 'art'; we need the semblance of goodness. In private we reveal our face, our self, our nature; we need goodness itself.'' To read Frame's biography of Montaigne is to see ''a man living what he reads.''

As Montaigne paraphrased the classics, so Frame paraphrases Montaigne - which , for a writer, is perhaps one experience of life eternal. With window open to the music of the cicada and the soft midnight breezes, I read Frame's Montaigne, and my summer is somehow complete.