The theme of the National Symphony Orchestra's summer festival--"Mozart and Marriage"--seemed on paper a notion in search of a composer, a cute parade of yesteryear's custom and costume to entice us gently away from the music and into the razzmatazz of how people got hitched a long time ago. But Artistic Director Christopher Hogwood had a larger design: bringing listeners closer to Mozart's unique creative vision and the world of his mind. (Richard Freed's extensive program notes were particularly valuable in this collaborative endeavor.)

Friday's program opened with Solfeggio No. 2, K. 393, an obscure vocal exercise Mozart wrote for and dedicated to his wife, Constanza, as a wedding gift. Sung admirably by Amy Wagar, the piece is loaded with roulades and registral leaps within phrases, a sure mark of Mozart's mature writing.

The celebrated Serenade, K. 361 ("Gran Partita"), was until recently wrongly dated, but scientific and scholarly research now shows its lineage as coinciding precisely with Mozart's wedding, and that it was also dedicated to Constanza and probably performed at their wedding reception. Written for paired wind instruments, the piece takes turns bubbling along as amiable entertainment, then deepening ineffably without breaking stride. Listeners who may have missed these subtleties could not overlook the astonishing breadth and profundity of some of the movements. Members of the NSO rose beautifully to the occasion, letting the music do most of the work but catching its spirit through buoyant textures and immaculate instrumental balance.

The unfinished Sonata for Piano and Violin, K. 403, yet another wedding present, is plainly expressive and affectionate (violinist Elisabeth Adkins and pianist Lisa Emenheiser Logan kept the voltage low), but the Sonata for Two Pianos, K. 448, is the best duo-piano piece ever written--airy contrapuntal lines flit back and forth with sublime ease, unusual even for Mozart. Pianists Logan and Edward Newman missed some of the fizz but otherwise got it right.

Saturday's program was less consistently revelatory: excerpts from "The Marriage of Figaro" and "Cosi Fan Tutte," and the Mass in C Minor, K. 427. The genesis of the Mass seems to relate to Mozart's engagement to Constanza, and may later have been a wedding gift. It is towering music that Hogwood conducted with his usual perception, drawing on J. Reilly Lewis's choral preparation of the Washington Bach Consort, alert musicians from the NSO and adequate young soloists. The opera excerpts were done concert-style using the same forces; the soloists were persuasive enough, and time will deepen their artistry.

CAPTION: Members of the NSO at Friday's "Mozart and Marriage" concert at the Kennedy Center.

CAPTION: With William Neil on harpsichord, soprano Amy Wager sings Mozart's Solfeggio No. 2.