"It is not enough to have a good mind; the main thing is to use it well." - Rene Descartes

Is this a question?

useing the mind for what purpose?
does well imply a moral wellness or a skillfull way at attaing that which you desire?
also god may be a invention of the devil, and the devil is a deciver.
etc etc..
is prehaps everything radically false - from some philosopher.

yes

That statement can be interpreted in too many ways that may even be conflicting.