Here is Ian MacLean’s article on Pascal at the Routledge Encyclopedia of Philosophy, London and New York 1998, as edited by ELLOPOS
Blaise Pascal was a mathematical prodigy who numbered among his early achievements an essay on conic sections and the invention of a calculating machine. In his early twenties he engaged in the vigorous European debate about the vacuum, undertaking, or causing to be undertaken, a series of experiments which helped to refute the traditional view that nature abhors a vacuum and setting out clearly the methodology of the new science.
In 1646 he came under the influence of Jansenism; this he seems to have rejected for a short time in the early 1650s, but he then underwent a profound spiritual experience which transformed his life and drew him into close association with leading Jansenists, with whom he collaborated in producing the polemical Lettres provinciales (1656-7).
At the same time he planned to write an apology for the Christian religion, but ill-health so affected his final years that this only survives in the fragmentary form of the Pensées (1670).
He made significant contributions to mathematics, especially in the fields of geometry, number theory and probability theory, and he also helped to describe the ’esprit géométrique’ which characterized the new science of the 1650s. He argued that geometry was superior to logic in that it could provide not only demonstrative procedures but also axioms from which to work; and he set down appropriate rules of argument.
His religious writings were published shortly after his death; many attempts have been made to reconstruct the apology which they encapsulate. It seems most likely that this would have fallen into two parts, the first setting out the wretchedness of humans without God, the second demonstrating the truth of Christianity and the felicity of the religious life.