 You are going to get the answers to all of your questions. Why didn't the angel just give them the gospel? Because the job of angels is not to preach the gospel. That is our job. Our job is to preach the gospel. How can they believe in Him unless they have heard about Him? How can they hear unless someone tells them? Ask Paul in Romans 10.14. So here we have Cornelius and the Lord is getting him ready. Meanwhile back in Joppa we have Simon Peter. God is prepping him.