Gustav Mahler said, “A symphony must be like the world—it must embrace everything.” This weekend, as grand finale to his first season as the Milwaukee Symphony’s new music director, Edo de Waart has chosen Mahler’s colossal Symphony No. 3.

Once, when Mahler was 5, his father left him sitting on a tree stump in the Bavarian forest and told him to wait there until he returned. Detained longer than expected, on his return the father found his little boy in a trance, so spellbound was he by the sights and sounds of nature.

The spellbinding power of nature pervades all of Mahler’s music, but especially his Third Symphony. His protégé, the conductor Bruno Walter, wrote: “It is not a ‘lover of nature’ who speaks here, but Nature herself transformed into music.”

Composed for large orchestra in the 1890s, the third of Mahler’s 10 symphonies runs nearly 100 minutes. It’s the longest symphony ever written, but there’s never a dull moment. Before he dropped the subtitles for its six movements, Mahler titled the first movement “Summer Marches In.” As long as some entire symphonies by other composers, it’s an exhilarating panorama of pantheist pandemonium.

The much shorter second movement, originally subtitled “What the Wildflowers Tell Me,” nicely reflects that delicate side of nature. The third movement, originally subtitled “What the Forest Animals Tell Me,” alternates between jaunty and rambunctious and features dreamy solos for posthorn, a rare instrument that is often substituted by an offstage trumpet.

In the fourth movement, marked misterioso, the human voice enters for the first time, as a mezzo-soprano sings a short passage from Thus Spoke Zarathustra. Who but Mahler would put Nietzsche’s pantheist version of eternity on equal footing with a Christian version of the same instinctual yearning?

The fifth movement juxtaposes a child’s na�ve faith with the philosopher’s struggle to turn doubt into affirmation. The shortest part of this six-part symphony, its text, taken from German folk poetry, depicts St. Peter’s own admission through heaven’s gate via repentance of his sins. Here a chorus of women’s and children’s voices cheerfully consoles the apostle and the rest of fallible humanity.

Then, without pause, the strings begin the sublime adagio final movement, which grows to ecstatic heights, ending in a dazzling climax punctuated by two timpani players. Mahler said this movement represents “the peak, the highest level from which one can view the world. I could almost call it ‘what God tells me,’ in the sense that God can only be comprehended as Love.”

The MSO, women from the MSO Chorus, the Milwaukee Children’s Choir and mezzo-soprano Kelley O’Connor will perform Mahler’s Third Symphony conducted by Edo de Waart in Uihlein Hall, 8 p.m. June 4-5 and 2:30 p.m. June 6.