For he counteracts the Devil, who is Death, by brisking about the life.

Smart’s line frames lively, embodied vitality—“brisking about the life”—as a spiritual resistance to despair and mortality. By equating “the Devil” with “Death,” the speaker treats death not only as an end but as an adversarial force that deadens the spirit in advance through fear, inertia, or gloom. The “he” (likely a figure whose energetic movement or joyful animation is being described) “counteracts” this force by actively inhabiting life: motion, cheer, and attentiveness become moral or devotional acts. The phrasing suggests a theology in which praise and liveliness are not frivolous but protective, a way of keeping the soul oriented toward life and (implicitly) toward God rather than toward nihilism.