Pascal's wager and Descartes's doubt: The heart has its reasons which reason knows nothing of!

Le cœur a ses raisons, que la raison ne connaît point. On le sent en mille choses. C'est le cœur qui sent Dieu, et non la raison. Voilà ce que c'est que la foi parfaite, Dieu sensible au cœur.

The heart has its reasons, which Reason does not know. We feel it in a thousand things. It is the heart which feels God, and not Reason. This, then, is perfect faith: God felt in the heart.
~Blaise Pascal

As exemplified in the argument above, Pascal firmly believed that to understand God, we need belief, which cannot be understood with reason. 

On the other hand, Descartes gave the argument:

"God has placed within us the idea of himself as a craftsman’s stamp on his work."

 Further, he had a penchant for doubt, and therefore wouldn't take belief in God as simply a wager:

Of course, on another note:

But whatever  be their difference of opinion, they were brilliant mathematicians!