One might compare the journey of the soul to mystical union, by way of pure faith, to the journey of a car on a dark highway. The only way the driver can keep to the road is by using his headlights. So in the mystical life, reason has its function. The way of faith is necessarily obscure. We drive by night. Nevertheless our reason penetrates the darkness enough to show us a little of the road ahead. It is by the light of reason that we interpret the signposts and make out the landmarks along our way.
Those who misunderstand Saint John of the Cross imagine that the way of nada is like driving by night, without any headlights whatever. This is a dangerous misunderstanding of the saint's doctrine.

Ch. X : Reason in the Life of Contemplation, p. 114. - The Ascent to Truth (1951)