The answer is that we are to look on each individual, not as a unit separated from the rest of the world, but as being integrally united with all of Creation. Rabbi Kook writes:
The nature of the world and of every individual creature, the entire sweep of human history and the life of every person, and his deeds, must be viewed from one all-encompassing perspective, as one unity made up of many parts… (Orot HaT’shuva, 4:4).
A man is not a fragmented being disconnected from the past and the future. He is part of the continuity of generations. He is a part of his national history and a sweeping world drama. In the same way that he is a product of his past, he is also the seed of the future. When a man sees himself in this wider perspective, the t’shuva he does for personal sins is magnified by his connection to all generations. Thus, his personal t’shuva is uplifted by the general t’shuva of the world, which strengthens his own drive to do good. This merging of an individual’s t’shuva with the mighty stream of the universal will for goodness is the source of the great joy which t’shuva always brings.
T’shuva comes forth from the profoundest depths, from the vast depths where the individual is not a separate entity, but rather a continuation of the greatness which pervades universal existence. The yearning for t’shuva (on a personal level) is connected to the world’s yearning for t’shuva at its most exalted source. And since the great current of the flow of life’s yearning is directed toward doing good, immediately many streams flow through all of existence to reveal goodness and to bring benefit to all (Ibid, 6:1).
For example, as a wheel axis spins, the spokes and the whole wheel spins with it. So too, a person who steals should not look at his theft as his own personal dilemma, he should see his stealing as something that damages the moral environment around him, and this adds evil to the society where he lives, and this increases the evil in the world. When he starts returning the money he took, he adds goodness to the world and brings all of existence closer to moral perfection. Like a stone thrown into a pool, his individual t’shuva sends waves of t’shuva rippling through all realms of life, from his family and immediate surroundings, to his community, his nation, and the world. Because his soul is attached to the soul of the world, in purifying his soul, he helps purify all realms of being.
Thus, Rabbi Kook writes that it is impossible to quantify the importance of practical t’shuva, and the correcting of one’s behavior in accordance with the Torah, which raises the soul of the individual and the soul of the community to higher and higher levels. Every step along the way contains myriads of ideals and horizons of light.
This understanding led our Sages to say that “Great is t’shuva, for it brings healing to the world,” (Yoma 86A) and “even one individual who repents is forgiven and the whole world is forgiven with him” (Ibid 86B).
The more we contemplate to what extent the smallest details of existence, the spiritual and the material, are microcosms containing the general principles, and understand that every small detail bears imprints of greatness in the depths of its being, we will no longer wonder about the secret of t’shuva which so deeply penetrates man’s soul, encompassing him from the beginning of his thoughts and beliefs to the most exacting details of his deeds and character (Orot HaT’shuva, 11:4).
When a man understands that his personal t’shuva advances the redemption process of the world, his motivation to mend his own life is enhanced. His own personal t’shuva expands beyond his life’s limited boundaries and brings benefit to all of mankind. No longer dwelling on escaping his own personal darkness, he altruistically yearns to bring greater illumination to the world. This is the zenith of t’shuva.