Why did Israel see themselves as distinct from other nations?
Israel viewed themselves as distinct because God had made them a set-apart, covenant people from their beginning in Egypt. He placed a division between them and the Egyptians, declared them separated unto Him, and called them a kingdom of priests, a truth reinforced throughout their history as a nation.
Les explains that this was not a put-down on the Jewish people but a national phenomenon: Israel had it pounded into them ever since they became a nation in Egypt that they were a set-apart people. They were God's covenant people. God told them in Egypt He would put a division between them and the Egyptians, and Deuteronomy says they were a separated people unto Him. Exodus chapter 19 calls them a kingdom of priests. Les notes this carried all the way into Paul's day, so when Paul began going to the Gentiles, they hated him for it. In Acts 22, Paul speaks to a great Jewish crowd in Jerusalem under Roman protective custody, rehearsing his salvation on the road to Damascus, and they would not receive his testimony concerning Jesus.