The nationalists of Italy wanted unity and resented the role of the Papacy in preventing this from happening. Wars were fought over control of the papal states, citizens wanted their own government, not to be led only by the church. It is only recently that historians have really found the impact and importance of religion in the Renaissance history. There have been a large number of studies that have been inspired by gaining an understanding of the relationship between the relationship of the church and politics.
Humanism came about because there was religion, this was a way to separate oneself from The Great Chain of Being, the church, and the fear of going to hell, into a place of one self and seeing one's own potential for greatness. No longer were they bound by their birth, their nobility, or lack thereof, but they are an individual who can worship God in their own way, and obtain salvation without the approval of a Priest.
Since 1883, records have been available at the Vatican, exposing the true role and power of the Church during the Renaissance. Paganism, just as Humanism, was started as a break off of the church. Everything in some way or form revolved and evolved from the church, and involved the Pope with secular, political, and even war issues. The Papal states were run by the church, and fought for their freedom to become a city-state, with their own elected government.
Up until the last century, religion and the Renaissance were kept separate, not understanding the involvement of one with the other. There are no longer any boundaries separating religion and the culture of the Renaissance. Religion influenced the lives of every living person, whether they were Christian, Jew, or Atheist. No longer can the church remain in the margins, but need to be out as a major part of history.