Nobody’s perfect, but as people get older they get better. Why repent when we’re young and we’re still likely to do wrong? Wouldn’t it be better to wait till we’re older and naturally stop transgressing?
This reasoning may seem sound, but it’s totally wrong. Firstly, nobody knows when they’ll die. So if one waits, it may be too late. Secondly, there’s no reason to think people become better with age. On the contrary, most people become even more fixed in their ways as they get older.
In his youth, Rabbi Shimon ben Lakish was a bandit. But he returned to G‑d wholeheartedly and for the rest of his life he was engaged in the study of Torah and the practice of mitzvot, and his teshuva was accepted.
The Midrash relates (Pd’RE 43) that on the day of his death, two of Rabbi Shimon’s erstwhile friends who had remained robbers all their lives also died. While Rabbi Shimon ben Lakish was granted entry to Eden, the other two were consigned to the abyss. They cried, “G‑d is there favoritism before You?” G‑d replied, “He repented before he died.” They retorted, “Spare us punishment and we’ll also repent!” G‑d answered, “Now it’s too late. Teshuva is only possible till the day of death.”
The Midrash explains this with a parable. To what might the matter be compared? To a person who departs to sea. If he fails to bring along bread and water, he will not find them at sea. Or to a person who traverses a desert. Should he fail to make provision before departing, he’ll find no food or drink in the wilderness. Likewise, if a person fails to do teshuva during his lifetime, it is no longer possible for him to do so after death.
Our Sages taught (Shabbat 153a), “Rabbi Eliezer said, ‘Repent one day before your death’. His disciples asked him, ‘Does a person then know on what day he’ll die?’ So he said to them, ‘All the more so. Let him repent today lest he die tomorrow, so that all his days may pass in teshuva!’”