"Though Peter was not by training or inclination an overly scrupulous Jew, and though as a Christian his inherited prejudices were gradually wearing thin, he was not prepared to go so far as to minister directly to Gentiles. A special revelation was necessary for that, and Luke now tells how God took the initiative in overcoming Peter"s reluctance." [1][source]
The original Greek, Roman, and Jewish readers of Acts all put much stock in dreams, visions, and oracles. They believed they came from the gods, or the true God in the case of Jews. So it is not surprising that Luke put much emphasis on these events in his conversion stories of Saul and Cornelius. This would have put the divine sanction for Christianity beyond dispute in the readers" minds. [2][source]