Blaise Pascal was a Catholic; specifically a convert to Jansenism (in 1646 as far as I know). Jansenism was a sect, like the Jesuits are a sect, of Catholicism.

William Doyle has written:

'The Oxford history of the French Revolution' -- subject(s): History

'Jansenism' -- subject(s): Jansenists, France, History, Church history

This is a huge subject, well outside the scope of a quick answer site like WikiAnswers. There were many problems in the Church at this time, from a group who wanted to be "enlightened" from some monks at the abbey of St. Germain in Paris complaining of their monastic discipline to French seminary students rioting to be allowed to wear wigs and attend the theater. One of the major problems in the Church at that time was the raise of Jansenism, the only major heresy since protestantism. So you have the rise of Jansenism, the suppression of the Jesuits (the main foes of the Jansenist heresy) and the horrible attacks on the Church with the French revolution. For a more complete survey, I would recommend James Hitchcock's book, History of the Catholic Church, or Diane Moczar's book, The Church Under Attack.

In twenty centuries, there have been way more than four reasons. If you check out the link below, you will find all the great heresies, starting with the The Circumcisers (1st Century) and Gnosticism (1st and 2nd Centuries) clear up through Protestantism (16th Century) and Jansenism (17th Century). In the early 21st century we are still dealing with Protestantism and Modernism.

Jansensism was a somewhat conservative and restrictive religious sect within Roman Catholicism. It originated in the Netherlands ( as did the Huguenot movement) but spread to France. Needless to say it no longer exists. The Jansenists taking the ( Lord I am not worthy) hymn-lyric literally, tended to discourage frequent use of the sacraments by laymen. They were pretty conservative and tended somewhat towards a predestination angle also. look them up! Blaise Pascal, the scientist and mathematician , belonged to this sect.