Paganism and Christianity
Paganism has different definitions; some will say paganism is any religion that isn't one of the Abrahamic religions (Islam, Christianity, or Judaism), while others will say paganism is a religion that follows a more polytheistic view of deity and seeks to revive the old ways of our ancestors. Paganism is an umbrella term, meaning it covers a wide range of religions and belief systems.
Christianity is one of the three major world religions and is one of the Abrahamic religions. Its roots are embedded in the Middle East, and its furthest beginnings reach back to the time of Abraham. This religion is based off of the Holy Bible, which is a collection of ancient books selected and compiled by a group of religious officials and Constantine in the 300s AD. Christianity is also an umbrella term in that there are hundreds of branches of Christianity, including but not limited to: Catholicism, Baptist, Lutheran, Methodist, Greek Orthodox, 7th Day Adventist, Mormon, Pentecostal, and more.
The roots of Christianity are interlaced with some of the most ancient pagan traditions and elements, mainly because the Church gained power through conversion. In order to convert the people of Europe (and the world) from their pagan beliefs, they either had to turn them against their beliefs by fear or accept and adopt some of their beliefs into the Christian religion.
Within the Catholic tradition of Christianity, one would be remiss to deny the pagan elements of a Catholic mass. The ritual of taking communion, with the round wafer (or bread), is an ancient practice of worshiping sun gods such as Ba'al and Osiris. The round wafer was a representation of the sun itself. When one ate the round bread or wafer, one was taking the sun into oneself. This tradition seemingly carried over into Christianity as the holy communion and taking the "Son" of God into oneself in celebration of him giving his life. Not to mention the "monstrance" used to hold the blessed sacrament is often gold and resembles the sun itself.
Water is one of the basic natural elements that was often worshiped in pre-Christian pagan times. Pagans believed that water had a "cleansing" power, not just physically but also mentally and spiritually. They would bathe and "cleanse" themselves and their children in sacred springs, rivers, and wells. This practice carried through to Christianity in the form of Holy Water, christenings, and baptisms.
Europeans were pagans for thousands of years and much longer than they were Christians, and some of these practices and beliefs are too ingrained in collective memory and DNA to fully eradicate with any newer religion or lack thereof.
Many of the oldest Catholic churches and monasteries in Europe and elsewhere throughout the world were built upon the ancient pagan sites. These were places where the pagan people worshiped their many gods and ancestors, and when the Church took over it was decided to knock down the pagan temples and replace them with Churches. The idea being that it would make it easier for the pagans to convert if they could still worship at their sacred pagan sites. Some of these pagan statues and symbols can still be seen in the oldest of Churches.