"To be born of the Holy Spirit is to be like to God with no stain of imperfection.
If the sun's rays strike a window, but the window is stained and dirty, the sun cannot shine through in the same way it would have done if the window was clean and spotless. All depends, not on the sun, but on the window. If the latter were perfectly clear the sun's rays would transform it, letting it reflect the light, even though the window preserves its distinct identity.
The soul resembles the window. By resigning itself to God, removing from itself every spot and stain of attachment to creatures and keeping the will united to God, it becomes immediately enlightened and transformed into him.
There cannot be perfect transformation without perfect pureness.
That soul which does not attain to the degree of purity corresponding with the light and vocation it has received from God can never be wholly content and at peace."
- St. John of the Cross