Musar para sa 1 Cronica 29:15

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.

And behold, the matter of distress is something entrusted to the heart. And the “nearby inclination” [i.e. the Yetzer Hara] reverses things and brings sorrow over the vanities of this world, while the sorrow of Heaven is discarded from the heart; [he is] neither pained nor aware. And the pure man should strengthen himself with pure thoughts to do each thing at its proper time in its proper manner, not replacing or substituting it, and he who comes to purify receives [heavenly] assistance (Shabbat 104a). And know that which is written in Ben Sira (Yevamot 63b) “do not suffer from tomorrow’s trouble etc.”. And since our days are a shadow on the earth [I Chronicles 29:15], what is the benefit to man in all his toils if his life will be [one of] sorrow? There is no good for man unless he is happy with his portion, trusts in the Name [i.e. Hashem], and does good [deeds].