The poem sets two scenes side by side. In the first line, a child "killed his melancholy out of doors": sadness is dealt with simply, by going outside. It sounds quick and almost innocent, though the word "killed" is surprisingly blunt for something so gentle.
Then the speaker takes over, and the tone shifts. Instead of going outdoors, they hear voices giving instructions: to "turn," to "talk with a knave," to "give." These commands are oddly varied. Turning might mean changing direction or changing one's mind, talking with a knave suggests mixing with someone untrustworthy, and giving points toward generosity or surrender. The poem doesn't say where the voices come from or whether the speaker obeys.
The mood is quiet, a little uneasy, and open-ended. The child's cure seems easy, while the adult's is tangled up with advice and temptation. The poem suggests that the speaker's melancholy isn't so simply left behind, and the short, clipped lines leave that tension unresolved.