The creation of the universe was a tight squeeze, according to Kabbalistic myth. Before God could conjure Heaven and Earth, he had to make space for his hulking omnipresence through a divine act of self-compression. Now, anyone can get a sense of what that felt like by visiting SFMOMA’s long-awaited new rooftop garden.

The opportunity comes courtesy of Barnett Newman, one of the most spiritual mid-20th-century abstract expressionists, whose final titled work, Zim Zum I (1969), was inspired by the Kabbalistic concept of godly compression known as tzimtzum. Two zigzag plates of Cor-Ten steel, each eight feet tall and weighing a couple of tons, face each other with only enough room between for an adult to wriggle through—a sculptural invasion of personal space that compellingly renders a mystical idea physical.

Zim Zum I will be unfamiliar to most people on their first visit to the rooftop garden, because sculptures of this scale spend much of their time in storage: Museum collections, like gods, have a tendency to sprawl and are stashed mostly in off-limits sub-basements. The garden also brings other important works out into the open, most notably Kiki Smith’s Virgin Mary, a life-size, flayed female figure cast in bronze, and Mario Merz’s The Lens of Rotterdam, a sort of all-weather igloo made of sheet glass and clamps.

Yet the collection is lacking. The problem is not so much that the half dozen strong works are crowded in with a number of weak ones—such as Henry Moore’s humdrum Large Torso: Arch—as it is that none of them actively engage their outdoor setting. The natural light is nice, of course, but at present the rooftop is essentially an annex, slightly relieving the permanent collection’s tight squeeze without expanding the museum’s reach. A garden is not just another room. To flourish, it must also be a realm for new, site-specific commissions that make use of the sun and rain and are alive to the outdoors. San Francisco Museum of Modern Art, 151 3rd St., S.F., 415-357-4000, sfmoma.org