In the name (en tōi onomati). The healing power is in that name (Page) and Peter says so. Cf. Luk 9:49; Luk 10:17; Act 4:7, Act 4:10; Act 19:27; Act 16:18.
Walk (peripatei). Present imperative, inchoative idea, begin to walk and then go on walking. But the beggar does not budge. He knows that he cannot walk.