Here is a beautiful description of the relationship between faith and reason in the life of a believer from Turretin 1.1.9.15:

He does not therefore mean to take away reason entirely because grace does not destroy, but perfects nature. He only wishes it to serve and be a handmaid to faith and as such to obey, not to govern its mistress; that it mapy be in subjection and not entirely discarded, that it may be not the foundation, but the defender of faith and embrace, contend for and adorn the faith already established.