Rav Kook on Teshuvah:

Teshuvah (returning to God) is basically returning to your original state, to the Root of life and higher existence... It is only through the great truth of returning to oneself that you, the nation, the world, all of the worlds, and all of existence, will return to its Maker, to be illuminated by the light of life, [Orot Ha Teshuvah 15;10].

Sudden teshuvah results from a spiritual bolt of illumination which enters the soul. All at once, you recognize the ugliness and evil of sin, and you are transformed into a new being. Already, you feel with yourself a total change for the good. This type of teshuvah derives from a certain unique inner power of the soul, from some great spiritual influence whose ways are best sought in the depths of life's mysteries....

There is also a gradual type of teshuvah, the change from the depths of sin to goodness is not inspired by a brilliant flash of light in your innermost self, but by the feeling that your behavior, lifestyle, thoughts and desires must be improved. When you follow this path, you gradually straighten your ways, mend your character, improve your behavior and teach yourself how to improve more and more until you reach the high level of refinement and perfection.

[Of these two types of teshuvah] the higher teshuvah is that which results from a lighting-like flash of goodness. This comes from the Divine Good which dwells in all worlds. It is the light of God Who is the life of all the worlds. With this illumination the noble soul of all existence is pictured before us in all of its splendor and oneness. The only limit to this illumination is the limit of placed upon it by your own heart, for you cannot grasp more than your heart is ready to absorb.

What this illumination reveals is that everything is so good and upright, and that this uprightness and goodness is within you as well; it arises from your being in harmony with everything. If you knew this you would see this. Your sense of being severed from the wholeness of existence, your feeling that you are a strange fragment scattered into nothingness like dust is a delusion arising from your failure to realize the unity and harmony of all things. When you recognize this, which is truly a divine recognition, then your teshuvah flows out of love, in the life of the individual and in the life of humanity as a whole.