Why did God send Israel back into dispersion after the crucifixion?
Because Israel rejected the Messiah and then rejected the preaching of Peter and the Eleven in the years after the crucifixion, God sent them back into dispersion, especially after 70 A.D. and the Temple's destruction, while turning His primary dealings toward the Gentiles.
Les explains that after Israel rejected the Messiah and all of Peter's and the Eleven's preaching in the first few years after the crucifixion, God sent Israel back into dispersion, especially after 70 A.D. and the destruction of the Temple. In the meantime, God began doing the opposite: instead of dealing with Israel primarily, He turned primarily to the Gentiles, though individual Jews could still come into the body of Christ. This shift is seen in Acts chapter 9, where God saved Saul of Tarsus, the very man trying to destroy Him from Judaism. As Saul labored under blindness after the Damascus road experience, God told Ananias not to fear him, because He would send him far hence to the Gentiles, and he would suffer for His name's sake. So the Apostle Paul now comes in as the Apostle, and Les points to Romans chapter 11 verse 13.