Why did Peter say it was unlawful to keep company with Cornelius if he was set free?
Peter spoke that way because he had not been set free from the Law; he was still a Law-keeping Jew. Even after the vision and the Lord's prompting toward Cornelius, he arrived with trepidation and still viewed Jewish separation from other nations as unlawful to break. His statement reflected that unchanged legalistic mindset.
Les explains that Peter first had the vision of the sheet with creatures and was commanded, "Rise Peter, kill and eat." He refused, saying he had never eaten anything unclean, because he was a Law-keeping Jew who required kosher food. Later, Peter went to Cornelius's house with trepidation, and Les pictures the Lord pushing him the 80–90 miles from Joppa, much as Jonah had to be pushed. At Cornelius's door Peter still said it was unlawful for him, a Jew, to keep company with a man of another nation. Why would he say that if he was set free? Les says he was not set free; he was still a Law-keeping Jew. The same kind of believing Jews under Peter's control in Jerusalem maintained separation, were still temple worshipers, and remained legalistic, though they had recognized Christ as the Messiah.