Had God or Jesus already revealed to the Twelve that Israel would be set aside and the gospel of grace would go to the Gentiles during the Gospels?

No. During the four Gospels, neither God nor Jesus had revealed to the Twelve that Israel would be set aside, the temple taken away, or the gospel of grace sent to Gentiles. Not one word had been spoken about such a period. Instead, Jesus spoke of promises to the nation regarding His kingship.

Les explains that as you go through the four Gospels, there had not been one word spoken, even by Jesus to the twelve, about a period when God would set Israel aside, take away their temple, and go to the Gentiles with a gospel of grace. The disciples’ expectation was the promised kingdom and Jesus as their King. They did not know He was going to be crucified, so Peter could not have preached Christ crucified before it happened. In Luke 18:31, Jesus tells the twelve they go up to Jerusalem and all things written by the prophets concerning the Son of Man shall be accomplished, but this does not reveal Israel’s setting aside or the gospel of grace going to Gentiles.

Had God revealed during Jesus' earthly ministry that He would set Israel aside and take the gospel of grace to the Gentiles?

No. During Jesus’ earthly ministry, not one word had been spoken—even by Jesus to the twelve—that God would set Israel aside, remove their temple, and turn to the Gentiles with a gospel of grace. The Gospels instead show Jesus speaking of what was promised to the nation regarding His kingship.