This dark night is an inflowing of God into the soul to purify it of its habitual ignorances and imperfections, both natural and spiritual. Contemplatives call it infused contemplation and mystical theology, in which God instructs the soul secretly in the perfection of love, without any intervention on its part, and without its understanding in what this infused contemplation consists… How does it happen that the soul calls the divine light a dark night? … There are two reasons for this. The first is that the divine wisdom transcends by reason of its elevation the capacity of the soul, and for that reason is darkness for it. The second reason lies in the baseness and impurity of the soul, which makes the light painful, afflictive, and also dark for it… The divine and obscure light places clearly before it all its infidelities.
Saint John of the Cross