We wrote above that Reb Elazar ben Durdiya cried and did teshuvah, and a bas kol announced that he had earned Olam HaBa. The Gemara adds, "Rebbe cried and said, 'Some acquire Olam HaBa after years [of toil in avodas Hashem], and some acquire their portion in Olam HaBa in a moment.'"
This is a good opening for our next subject – the realization that one can do teshuvah in one moment. It takes just a second, and everything can be turned around. Elazar ben Durdiya was a grave sinner, but at a moment of inspiration, he did teshuvah, acquired Olam HaBa, and was called Rebbe.
The Rambam (Hilchos Teshuvah 2:2) states, "What is teshuvah? It is (1) to leave the sin, (2) to remove it from his thoughts, and (3) to be determined never to commit this sin again." So, teshuvah is a decision not to sin again. This is the essence of teshuvah, and such a decision can be made in a moment.
The Gemara (Kiddushin 49:) says that if a total rasha (גמור רשע) betroths a woman and says גמור צדיק שאני מנת על, "The marriage is contingent on me being a perfect tzaddik," we consider them married (מספק), because he may have had a thought of teshuvah while giving her the ring. This is another source that teshuvah can be done in a moment. One thought of teshuvah turns the person around from being a total rasha (rasha gamur) to a perfect tzaddik (tzaddik gamur).
The Gemara (Kiddushin 40:) states, "If one was a rasha his entire life and did teshuvah at the end of his life, his past bad deeds won't be mentioned anymore."
