Why did God permit Rome to destroy the city and temple?
God permitted Rome to destroy Jerusalem and the temple after a 40-year period of testing because Israel remained adamant in unbelief. The sovereign God allowed Rome's awful siege, the temple's destruction, and Israel's dispersion among the nations. This judgment followed the crucifixion and the book of Acts period, when Israel rejected the offered kingdom.
Les explains that from the crucifixion until the Roman army destroyed the temple was 40 years. The book of Acts covers that 40-year period, during which God was still dealing with His covenant people even though He was beginning to go to the Gentiles before the 40 years ended. In Israel's history, 40 years had always been a period of testing, and at the end of it Israel was still adamant in unbelief. Therefore the sovereign God permitted Rome to come in, destroy the city in the most awful siege in ancient history, and destroy the temple. Israel was then sent into dispersion among all the nations, a dispersion that has begun to end in our lifetime but has not fully ended for the most part. Earlier, Les notes, Israel's repentance and baptism were the prerequisite for the King and the kingdom, but God knew Israel would not do it and would go to the Gentiles without Israel.