How does the book of Acts relate to Israel and the Gentiles during its 40-year timeframe?
The book of Acts spans the 40 years from the crucifixion to Rome's destruction of the temple. During it, God was still dealing with His covenant people Israel, while also beginning to turn to the Gentiles before the 40 years ended. At the end, Israel remained in unbelief.
Les teaches that from the crucifixion until the Roman army destroyed the temple was 40 years, and the book of Acts is that 40-year period. He explains that God was still dealing with His covenant people Israel, even though He would start going to the Gentiles before the 40 years were up. Israel's valid offer required every Jew to repent and be baptized with water, as Acts 2:38 was still appropriate; then Christ would have ushered in the tribulation, lifted the curse, and brought in the kingdom, and Israel could have evangelized the nations. But God knew Israel would not do it, so He would go to the Gentiles without Israel. At the end of the 40 years, Israel was still adamant in unbelief; therefore God permitted Rome to destroy the city and temple in an awful siege, and Israel was dispersed among all nations, a dispersion that has begun to end but has not fully ended.