Correction: once in 5 million years. God came to earth as a tiny baby to change the world forever.
God’s timing was perfect. NEVER had there been anything like the Pax Romana. Under Roman rule, the ‘known’ world was at peace, as Rome had conquered all her enemies. This meant that one could go from (what is now) the UK, into Asia and Africa and there was peace and a common language, in addition to local languages. The Gospel could then be taught throughout the Roman Empire. NEVER had so many lands and people been at peace! NEVER could so many disparate peoples been introduced to GOD and His plan for Salvation!
Paul’s three year imprisonment in Rome meant that he could preach to the ‘movers and shakers’ in Rome. He was apparently guarded by the Praetorian Guard, two men at a time, in four hour shifts. His preaching had an effect! Those Praetorians who heard and believed, soon spread the teaching among the upper crust of Roman society, to the point that Christianity was accepted as a religion in the Empire less than 300 years after Jesus’ Resurrection and accepted as the ‘official’ religion of the Empire 350 years after Jesus’ Resurrection!