Has Israel been forgiven for rejecting and killing their Messiah at this point in Acts?
At this point in Acts, Israel had not been forgiven for rejecting and killing their Messiah. Peter addresses the men of Israel in Acts 3, charging them with delivering up, denying, and killing the Prince of Life, and he calls them to repent.
Les teaches that Acts 3 is addressed specifically to the men of Israel, not to the church. They had just witnessed the healing of the lame man, and Peter declares that the God of Abraham, Isaac, and Jacob glorified His Son Jesus, whom they delivered up and denied before Pilate. They denied the Holy One and the Just One and killed the Prince of Life. When Peter says 'Repent' in verse 19, the issue is that they had rejected, killed, and murdered their Messiah. Les emphasizes this was still on God's mind: the nation of Israel had not yet been forgiven for rejecting, killing, and crucifying their Messiah. He also cautions that this must not be used as an excuse for anti-Semitism, since many religions have wrongly accused the Jew of being the God killers.