The concept of a second coming for Jesus is two things:
1) It is a get-out clause for any failed messiah, and something that can give proof anything cannot lend support to anything.
2) It is an admission that Jesus didn’t get the job done. Do you know what this means? Jesus did not fulfil the clear messianic prophecies. He didn’t measure up to the full criteria needed to be that promised king. Therefore he can’t be the messiah prophesied of in the Jewish Scripture. Why not? I told you, the christians tell you by using the “second coming” “defense”: he didn’t get the job done.