"Toward heaven" but never to, never all the way. Frost fears transcendence. Despite all the apparent moralizing ("earth's the right place for love"), this passage is one of the most skeptical in Frost. He contemplates a moment when the soul may become completely absorbed into a union with the divine. But he is earthbound, limited, afraid. No sooner does he wish to get away from earth than he thinks of "fate" - rather than God. And what might be a mystical experience turns into a fear of death, a fear that he would be snatched away "not to return." He rejects the unknown, the love of God, because he cannot know it, and he clings to the finite: "Earth's the right place for love."
From "Going and Coming Back: Robert Frost’s Religious Poetry." South Atlantic Quarterly (Autumn 1974).