"Easy. Paul could do miracles to give prove:
(Acts 14:8-11) 8 Now in Lysʹtra there was a man sitting down whose feet were crippled. He was lame from birth and had never walked. 9 This man was listening to Paul as he was speaking. Paul, looking intently at him and seeing that he had faith to be made well, 10 said with a loud voice: “Stand up on your feet.” So the man leaped up and began walking. 11 When the crowds saw what Paul had done, they cried out in the Lyc·a·oʹni·an language: “The gods have become like humans and have come down to us!”
That hardly proved that Paul was hand picked by Jesus. The Lycaonians were pagan and believed in many gods. They thought Paul and company were gods.They called Barnabas Zeus, and Paul Hermes. And even when Paul explained who he was they still tried to sacrifice to him. Obviously nothing that Paul said convinced them he was not Hermes.
Which proves my point; you are going to believe what you want to believe, regardless of evidence. No matter how many miracles Jesus performed and how many prophecies regarding himself he fulfilled, people still did not believe he was the messiah.