There's a reason why early christian depictions of Christ make him appear as an Italian or other Southern European. It's because the roots of the phenomenal growth of Christianity were in the Roman Empire. Jesus was a counter culture boogeyman that the Hebrews used to scare their tormentors and Christianity never really took off in the "Holy Land" until the Romans accepted monotheism and Christianity in particular as a part of their own culture because it had proven so effective as a tool against the authorities during its early days.
With it, you could get people in a gladitatorial arena to face starving lions armed with nothing more than their faith, showing more bravery than the most galant of military Men. This opiate only grew in power as it spread and the leadership of the Republic sought to avail themselves of that power.
If I'm selling moon pies in China, there's going to be a picture of a Chinaman eating a moon pie in my sales pitch. Same theory for selling Christianity in Europe..there were similar marketing drives going on in other parts of Africa and throughout the Mediterranian and Indian Ocean trade routes but they didn't have near the success of the Roman campaign because Christianity followed the army and the trade routes which at that time was everything North of 2nd cataract of the Nile and West of the Eurasian Steppe.