His lucid exposition interested every one in the abstruse problem, Is man's freedom such as not to render grace superfluous?
But Pascal perceived that casuistry was not the only enemy that menaced the true spirit of religion for which Jansenism stood.

He came to realise that Cartesianism, to which he was at first drawn, was profoundly opposed to the fundamental views of Christianity.

His Pensees are the fragments of a work which he designed in defence of religion, and it is easy to see that this defence was to be specially directed against the ideas of Descartes.
Pascal was perfectly right about the Cartesian conception of the Universe, though Descartes might pretend to mitigate its tendencies, and his fervent disciple, Malebranche, might attempt to prove that it was more or less reconcilable with orthodox doctrine.

We need not trouble about the special metaphysical tenets of Descartes.

The two axioms which he launched upon the world--the supremacy of reason, and the invariability of natural laws--struck directly at the foundations of orthodoxy.