Vicious tendencies are produced only by our corrupt nature, and it is very difficult to conquer them without mental prayer; but by means of this prayer we can overcome them easily. The soul in mental prayer is like iron in the fire: when the iron is cold, it is difficult to work; but when it is put into the fire, it becomes soft and allows itself to be easily worked: so it is with the soul… When a soul comes out from mental prayer it is quite changed.
–Saint Alphonsus Liguori (1696-1787)