Pascal was attacking Cartesianism when he made his memorable attempt to discredit the authority of reason, by showing that it is feeble and deceptive.

It was a natural consequence of his changed attitude that he should speak (in the Pensees) in a much less confident tone about the march of science than he had spoken in the passage which I quoted above.

And it was natural that he should be pessimistic about social improvement, and that, keeping his eyes fixed on his central fact that Christianity is the goal of history, he should take only a slight and subsidiary interest in amelioration.
The preponderant influence of Jansenism only began to wane during the last twenty years of the seventeenth century, and till then it seems to have been successful in counteracting the diffusion of the Cartesian ideas.

Cartesianism begins to become active and powerful when Jansenism is beginning to decline.

And it is just then that the idea of Progress begins definitely to emerge.