This is a poem about how mankind, represented by the "Man" of the poem, tries to free himself from a wasteful, unfulfilling life, a life led in pursuit of money, and a life characterized by conflicts and bigotry. Stevie Smith, of course, lived through both world wars and so would understandably have become disillusioned with the plight of mankind. Stevie Smith herself indicated that this was what the poem was about in one of her novels, The Holiday, which you can read a little bit about in the article linked below.
This unfulfilling, wasteful life from which "Man" tries to escape is represented by the mountains in the poem, perhaps because mountains symbolize the barriers mankind has, metaphorically, built for itself.
The speaker in the poem has a sympathetic attitude toward "Man," almost as if the speaker is God: "Is there no one to help my creature / Where he languishes?" The possessive pronoun here ("my") implies that the speaker feels also a sense of responsibility toward "Man."
The last two stanzas suggest how difficult it will be for mankind to free itself from the old way of living and move into another. The "Man" in the poem stumbles and falls and "lies with his head in the rubble." And the speaker concludes with the question, "Will he come out of the mountains?" and the answer, "It's touch and go." The phrase "touch and go" means that it is uncertain and that the chances change from moment to moment. The poem finishes with this uncertainty, but Smith's sympathetic portrayal of "Man" encourages us, as readers, to hope that "Man" does indeed manage to free himself from the mountains and from a life which has made him "bowed by sorrow and fret."