In context:
A love of the grease and a feel for the gist, the habit of compromise even at the cost of absolute clarity, a restatement of technical argument in emphatic simplicities, clarity achieved and helpful ambiguity sought—these were the heart of Lincoln’s style, and of his soul. They explain why we still argue about him: he said very clear things against slavery—and, for a time at least, he was ready to keep the slaves if he could find a bargain to keep the South in the Union. Law is the practice of rules in a context of deals, and Lincoln believed in both.
Curiously, Gopnik's phrase works just as well inverted, though perhaps better if Regulation is substituted as the subject: "Regulation is the practice of deals in a context of rules."
