We realize that there is no true life except in conversion and that there is no other means of entering into life: unless you are converted and become as little children, you shall not enter the kingdom of heaven.
Clearly, then, the conversion of souls is the working of the divine, not the human, voice. May I suggest then that you prick up the ears of your heart in order to hear this inner voice and that you make an effort to hear God speaking within rather than the man speaking without. For that is his voice, powerful and full of majesty, which shakes the wilderness, pierces all secret things and drives away the sluggishness of souls.
Nor do we have much difficulty in hearing this voice; the difficulty is rather in stopping our ears from hearing it. For that voice offers itself, presents itself, and never ceases to knock at the door of each of us.
Bernard of Clairvaux, Sermons on Conversion, CF 25, pp 31-33