The speaker is a kind of court functionary, someone who reads quickly and carelessly the "long sentences" of official documents or judgments, and who plays along with power. The image of a troll on the King's boat is telling: the speaker sees themselves as a rough, out-of-place creature who has slipped aboard among the powerful. Instead of challenging anything, they make "a pretty deal / of public sin," meaning they dress up wrongdoing in agreeable language.
The tone is dry and quietly self-mocking. The short line "fitting in" sounds like an excuse, and the final two lines make the price clear: "I gain a home. / They have me sing." Belonging comes with a catch. The speaker is comfortable, but also kept, and the singing suggests being made to perform, perhaps to praise. The mood is uneasy and wry, with a hint of shame under the neat, clipped phrasing.