Why might the construction of the roads have been so important to the spread christianity throughout the roman empire?

The construction of roads was most likely a very important factor in spreading Christianity throughout the Roman Empire because roads increased the connectedness of the Empire and allowed for trade and cultural diffusion to occur. With increased access there was greater exposure to Christianity which likely increased the number of followers within the Empire. 

The Roman roads have been important in the spread of Christianity because as you know the roads allowed merchants to travel and trade easily throughout the empire but not only were ideal goods traded but also beliefs and philosophy were exchanged and shared.