Christianity and Islam were spread by these Empires with the sword and those living in the effected areas had no choice other than to convert. To make the transition to the new religion easier they again built on the old pagan believes. These developments happened in times were life expectations were short, poverty and misery widespread so their message of a golden age (eschatology), a heaven where you could have a good afterlife or one with lots of virgins provided a welcome prospect for poor and uneducated people.
However, in all these developments, individual spirituality was further and further pushed away and instead organised religion was preached as a better (and only) alternative. People who did want to go back to basics and pointed to personal spirituality (as different from religious spirituality) were rapidly declared heretics and were persecuted and often burned at the stake.
Superstition remained the basis of the society where natural and environmental events as well as personal events such as illnesses, recovery were miracles or punishments of God or activities from the Devil. For most ordinary people being the rural people, the new religions basically became add on to the people’s pagan beliefs and traditions. Religion formalised this through rituals, rules, and regulations.
The religion institutions became real powerhouses and were involved in all aspects of the life of individuals, their societies, and economies. In western Europe, the Catholic Church grew into a multinational corporation – who also controlled most of the wealth of that time, happily supported by the secular rulers who equally profited from this situation.