Musar do Pirke Awot 2:15

And among the things for which a person is obligated to remember the day of death is in order that he not waste [time] and his hands not falter from the service of God, may He be blessed; that he remove sleep from his eyes to toil in Torah [study] and to contemplate fear of God, to refine the traits of his soul [so as] to reach levels of fear and love; and to think thoughts of how to enhance and beatify the commandments such that his soul should be a charm and a treasure - like the matter that is stated (Proverbs 10:8), "He whose heart is wise accepts commandments." For he will know and remember that the days are short - as our Rabbis, may their memory be blessed, said (Avot 2:15), "The day is short, and the work is plentiful, and the laborers are indolent, and the reward is great, and the Master of the house is insistent."

And the third [reason] is that the time decreases and the work is plentiful: The work of Torah [study], refinement of the soul and attainment of the virtues - such as love, fear and cleaving. As they, may their memory be blessed, said (Avot 2:15), "the day is short, and the work is plentiful."

For seven reasons should a man repent early while still in his youth when his power is strong. The first is that the labor needed to acquire Torah and reverence for God and all qualities that a man must possess is exceedingly great. And concerning this it is said, "The measure thereof is longer than the earth and broader than the sea" (Job 11:9). And, "The day is short" (Aboth 2:20). For this world is a very short day. "Like a shadow are our days upon the earth" (I Chron. 29:15). And our Sages, of blessed memory, said, "Not like the shadow of a wall and not like the shadow of a tree, but like the shadow of a bird in flight" (Gen. Rabbah 96:2). And as to the expression, "And the workers are lazy" (Aboth 2:20), this refers to a man who has within him the quality of laziness.

The third reason that a man should hasten to repent while still in his youth is that the time is so little and the work is so much — the work of studying the Torah, and the improvement of the soul, the attainment of good qualities such as love, reverence, and cleaving to God. As our Sages said, "The day is short, and the work is great" (Aboth 2:15).

The Mishnah continues by stating that neither serpent nor scorpion was ever reported to have inflicted harm on people in Jerusalem. We may also understand this in a spiritual sense, namely that the words (fire) of scholars (Avot 2, 15) do not harm the soul; should these scholars have been provoked however, their words have been compared in power to that of serpents and scorpions.