Human existence is brief and temporary, much like the life cycle of a plant that sprouts and fades within a single day. The sharp contrast between the dawn and the dusk serves as a powerful reminder of human fragility when measured against the eternal nature of God [אבן עזרא, מלבי״ם, ביאור שטיינזלץ].
The dawn represents the period of youth, a time of blossoming and vitality [מצודת ציון]. During these early years, a person flourishes, gathering strength and constantly renewing themselves, much like changing into fresh clothes [רד״ק, אבן עזרא, מאירי]. On a spiritual and moral level, this morning period signifies an awakening. It is a time when a young person might be inspired to pursue good deeds and seek a path of repentance.
However, this early growth is fragile and passes rapidly, failing to endure until the day's end [רש״י]. This transition can sometimes take a negative turn. Rather than maintaining their youthful inspiration, a person might abandon the good they initially embraced, exchanging it for a poorer path [אלשיך].
As the day transitions into evening, it mirrors the onset of old age [רד״ק, מצודת דוד, אלשיך]. Just as fresh, moist grass is beaten down by the relentless heat of the sun throughout the day until it completely dries out [מצודת ציון], human life slowly fades [רד״ק, מצודת דוד]. In this final stage, life is cut down and broken apart [רד״ק, מצודת ציון, ביאור שטיינזלץ]. Alternatively, this end is described as a state of crumbling, like something turning to dust in one's hand from sheer dryness [מאירי].
This physical withering carries a deep spiritual warning for a person's final years. Ideally, old age should be a time to disconnect from material pursuits and draw closer to God. Tragically, it often becomes a bleak period where a person forgets their mortality. Instead of growing spiritually, their good deeds and inner vitality simply dry up and are cut short [אלשיך].