And what does teshuvah consist of? [Repentance to the degree] that the One Who knows all that is hidden will testify that he will never again repeat this sin (Maimonides, Laws of Teshuvah 2:2).
"How can this be?" ask the commentaries. "Inasmuch as man always has free choice to do good or evil, to sin or not to sin, how can God testify that a person will never repeat a particular sin? Is this not a repudiation of one's free will?"
The answer to this came to me at a meeting of Alcoholics Anonymous, at which the speaker, a man who had been sober for twenty-one years, said, "The man I was drank. The man I was will drink again. But now I am a different man."
A sin does not occur in a vacuum. A person who is devout does not abruptly decide to eat treifah. A sin occurs when a person is in such a state that a particular act is not anathema to him.
Consequently, repentance is not complete if one merely regrets having done wrong. One must ask, "How did this sin ever come about? In what kind of a state was I that permitted me to commit this sin?"
True repentance thus consists of changing one's character to the point where, as the person is now, one can no longer even consider doing the forbidden act. Of course, the person's character may deteriorate - and if it does, he may sin again.
God does not testify that the person will never repeat the sin, but rather that his degree of repentance and correction of his character defects are such that, as long as he maintains his new status, he will not commit that sin.