The poem plays a clever trick with its central comparison. It opens by calling birth "mundane, a mere formality," then slides into a scene that seems to be a purchase: a manager hands over a key, a woman in a flowered dress looks on with a baby. Only gradually do we see that the "beast" with its chrome, tyres and handlebars is also treated as a newborn. The speaker touches it gingerly, lets his feelings "flow into him," and finally "nurses" it into the streets.
The speaker feels awe, nervousness and tenderness, like a new father unsure of his own hands. The buying of the machine and the arrival of a child blur together, so pride, responsibility and fear all mix. The mood is warm and hopeful, with a slight edge of anxiety in the last line, where he leads something precious into "chaos." The title, "Running in," fits: both the bike and the child must be carefully broken in.