Note 4 at Ac 10:5: It is very interesting that this angel told Cornelius to send to Joppa to get Peter to come preach Jesus to him. Didn't the angel know how to tell Cornelius to be born again? Of course he did, but he didn't have the authority to preach the Gospel. The Lord Jesus gave physical human beings, and them alone, power (or authority) to be His witnesses (Ac 1:8). If we don't witness, the angels won't do it for us (see note 4 at Ac 1:7).