In the name (εν τω ονοματ). The healing power is in that name (Page) and Peter says so. Cf. Luke 9:49; Luke 10:17; Acts 4:7; Acts 4:10; Acts 19:27; Acts 16:18.

Walk (περιπατε). Present imperative, inchoative idea, begin to walk and then go on walking. But the beggar does not budge. He knows that he cannot walk.