“There are many levels of repentance.
One person may need to make ever greater and more intense efforts towards Divine unity while another may desire no more than to be able to make an honest living.
True, there is also a matter of proportion -- the more one has been sunk in sin the greater the pressure to emerge.
Just as a dam holds back a body of water, the higher the dam the greater the power which can afterwards be extracted from release.
But all this means that the sinner has to go through all the intervening stages of growth and comprehension, and that the more he learns of the magnitude of his past transgressions, the more painful the knowledge and the more effective the transformation.
A person who has sinned for ten, twenty, or fifty years, feels the immense vacuum in that part of his life.
Although he strives desperately to fill it, there seems to be an emptiness that nothing can satisfy, and his past evildoing, even if thoroughly repented, becomes part of the structure of his soul in the opposite direction.
This is why it is said that, in a way, a true penitent, with that extra power of recollected sin, stands on the higher level then a tzaddik who has never sinned at all.
The nature of the transformation is more like a chemical change, a change of essence rather than a change of form or place.
Everything that was true of a person is transmuted into a different substance.”
From "Levels of Repentance," p. 39 in The Long Shorter Way by Rabbi Adin Steinsaltz
