Angels are typically used by God as his messengers (see Luke 1:11–20, Luke 1:26–38; Luke 2:9–14). The angel is thus sent to give a message to Cornelius. In this case the presence of the angel serves to underscore the fact that it is God’s plan and initiative which brings about the conversion of the first Gentile.1
3 About the ninth hour of the day he saw clearly in a vision an angel of God come in and say to him, “Cornelius.”