Musar su Deuteronomio 32:4

All this is evident and clear for G-d is a G-d of truth as Moshe Rabeinu, peace be unto him, said: "The Rock, His work is perfect; For all His ways are justice: A G-d of faithfulness and without iniquity, Just and right is He" (Deut. 32:4). For since the Holy One blessed be He desires justice, to ignore the bad would be just as much an injustice as to ignore the good. Therefore, if it is justice that He desires, then He must pay each man according to his ways and according to the fruits of his deeds to absolute exactness, whether for good or for bad. Thus "A G-d of faithfulness and without iniquity, Just and right is He" (Deut. 32:4) which our Sages of blessed memory explained [the dual terms]: "to the righteous and to the wicked" (Taanis 11a). For this is the trait [of justice]. He judges on every thing. He punishes every sin. And there is no escape.

Besides all this, all the free time he has left from his affairs, if he is wise, certainly he should not waste it. But rather to immediately grasp hold of it and not be lax in it, utilizing it to toil in the affairs of his soul and the improvement of his service of G-d.

Consider the severity of levity and its destructive power. For just like a shield smeared with oil deflects and drops arrows from him, causing them to fall to the ground, preventing them from reaching the body of the man, so too is levity before rebuke and reprimand. For with one act of levity or a little laughter, a man casts from himself a great many rousings and impressions that the heart was made to feel due to stimulation in seeing or hearing matters that awakened him to an accounting and examination of his deeds.