Okay, the first thing we have to realize is that Christianity came in to its position via the patronage of Constintine, who is pretty much cosidered the last great Roman emperor. Not only did he make Christianity his state religion but he also applied the Roman practice of assimilating other cultures to it. One of the great strengths of the Roman empire is that they managed to assemilate many different peoples and cultures and make them feel like they were part of the empire. This often involved absorbing versions of their religions and holidays into Roman culture. Christmas is the christian take on the holy day for the mithric solar cults, while Easter is the assemilation of fertility rite of the goddess Ester, thats were the eggs come from, fertility. Regardless of the source of reasons behind the differant rites and religions it seems people have always spent a great deal of time, effort and resouces in celebration of their deities and the ensuing rites. Most of the older artifacts even the most archaiac cultures are religiouse in nature and it's certainly no differant with christianity. One of the biggest sources of our knowledge in the history of architecture are the churches from bygone centuries they have often outsurvived evn fortifacations in many places. In a lot of ways the divine focus of the churches even pushed the technical aspects of building even futher ahead as people sought to create soaring arches and vaulted or cathedral ( it's in the name) ceilings to add to the grandure of their churches.
I also think its interesting to note the church intergrated a lot of the deities of polytheistic religions as saintes and angels. And lets face it, while we get a lot of our knowledge of the dark ages from church records they were also responsible for the destruction of a lot of older records that didn't jive with their world view.