Children, when they have long lived in ignorance, consider themselves happy. Because those who depend on their good works are, owing to their passions, improvident, they fall and become miserable when their life (in the world which they had gained by their good works) is finished.

In plain words: People who stay ignorant for a long time are like children who think they are happy. Those who rely only on their good deeds are driven by desires and do not see far ahead. When the heaven they earned runs out, they fall and become miserable.