What does Acts 11:6 mean?

Peter is relating a vision he had to the church leaders in Jerusalem. He had been in Joppa, near modern-day Tel Aviv, on the rooftop of Simon the Tanner. While praying, he got hungry and asked for some food. Before it arrived, he had a vision of a large sheet drifting down from heaven (Acts 10:9–11).

The original account in Acts 10:12 merely says the sheet had "all kinds of animals and reptiles and birds of the air"; Acts 10:14 infers some of them were not allowed as food per the Mosaic law (Leviticus 11). Here, Peter gets more specific. The law forbids pretty much every meat-eating animal, including carrion birds and birds of prey, anything with paws, and pigs. The law also forbids "the great lizard of any kind, the gecko, the monitor lizard, the lizard, the sand lizard, and the chameleon" (Leviticus 11:29–30).

When Peter was traveling with Jesus, he saw the Pharisees criticize Jesus and His disciples several times for their eating habits. First, because Jesus ate with sinners and tax collectors (Mark 2:15–17). Another time because the disciples were plucking wheat kernels on the Sabbath (Mark 2:23–28). And again, because the disciples didn't ceremonially wash their hands before they ate (Mark 7:1–5).

The "circumcision party" that is questioning Peter about why he ate with Gentiles are probably former Pharisees who now worship Jesus (Acts 11:2). In fact, they may still consider themselves Pharisees, since Jesus-worship is the natural fulfillment of Judaism. If Peter, who watched Jesus interact with Pharisees and their overly rigid food laws, needed a vision to understand the kosher laws are lifted, these legalistic Jewish-Jesus-followers are going to need a lot more convincing.