I thought I might comment on your question: is John Calvin’s time line on the emergence of statues, relics and “holy water” , as 500 AD, an accurate point in time. I believe the problem, in our current day and age, in recognizing when early church trends started to occur is that many of the historians from the first thousand years of church history wrote in Latin and most of us encounter just selected quotes in the  writings of Middle Ages authors like Calvin. Regarding when images (e.g. statutes), relics and “holy water” became embedded in Christian culture it’s hard to say however there are a few good indications. Constatine had consolidated power by 312 AD and the life stories of his mother, St. Helen, are focused around the discovery and preservation of relics and images from the time of Jesus Christ. Subsequently, Charlemagne became the Holy Roman Empire emperor at Christmas in 800 AD and the Byzantine rulers accepted this designation by 812. This consolidation actually strengthened the power of the Roman Catholic Popes and resulted in cannons which reference, in part, many of these issues. As reformed theology, Presbyterians, I think we look to the reformation’s great theologians, like John Calvin, who helped to define the gap between the will of God as presented to us in scripture and the Roman Catholic decrees of their papacy, at that time, which defined their perspective on relics, statutes, “holy water” as well as papal infalability. All were controversial issues of scriptural interpretation then as now.  The Roman Catholoic Church, in papal cannons (which are still in effect) from the Council of Trent, at the time of John Calvin, declared that any person who does not  believe these papal doctrines ( e.g. relics, statues, “holy water” ) is “anathema”, that is they are officially and ritually cursed by the Catholic Church. I personally would rather focus on points of agreement in Christian theology with all Christians however at the time of John Calvin there is no doubt that he could have been burned at a stake for his reformed theology views. So I guess I’d take 500 AD as as good a point in time to say statues, relics and “holy water” became a part of Christian worship. By the time of the first Crusades, the Templar Knights certainly became very wealthy in the relic trade.