1) Mental ability because Aristotle believed that there was nothing more important than contemplation in living a good life. There were also Sophists who were prominent teachers and famous for their rhetoric and speaking abilities in courts.
2) Many of the earliest members were from the Greek or Gentile communities in Macedonia, some of whom had been pagan. Some had been familiar with Jewish customs even though they were not Jewish. Some Jewish people also converted but the majority were Gentile. Many early Christians would travel or migrate through the Roman empire and, especially, Paul would write letters to various communities.
3) Mecca was an important religious centre because of the old sanctuary there, known as the Kabah. This place was taken care of by the prominent families of the area, known as the Quraysh tribe, who were also tradesmen and merchants. Thus, economy was tied closely with politics and religion.
4) Rome is on Italy which is a peninsula. Italy has nearly a 7600 km coastline which made it hospitable to ships from all parts of the region. It was easy to connect to from Northern Europe and from Africa.
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