Human life is often defined by exhausting labor, a lack of freedom, and a constant desire for rest and reward [ביאור שטיינזלץ]. This reality is captured through the imagery of hard-working laborers, expressing a deep, existential longing for a break from the heavy burdens of existence.
The primary approach among commentators is that this presents a picture of profound physical and mental exhaustion. A slave, bound to hard labor throughout the day, desperately longs for the evening shadows so he can finally rest from his toil [רש״י, מצודת דוד] and complete his chores [אבן עזרא]. Similarly, a hired worker labors all day and eagerly anticipates the sunset, hoping to finish his task and collect his earned wages [רש״י, מצודת דוד, ביאור שטיינזלץ]. The longing described is a deep desire and hope for the ultimate reward of one's difficult efforts [מצודת ציון, רלב״ג].
Within this comparison, there is a fundamental difference between the two types of workers. A slave is owned by his master and works on a fixed schedule, which is why he simply waits for the day to end. A hired worker, however, is employed for a specific task, and his freedom depends on actually completing it. This distinction highlights a painful reality regarding human suffering. When a person is sick, he is unable to work. If his life's purpose is measured by time, the days spent in illness are completely wasted. On the other hand, if his purpose depends on accomplishing a long spiritual mission, physical suffering halts the work of the soul and prevents him from ever reaching perfection [מלבי״ם].
A completely different perspective reverses this understanding, viewing the imagery not as a desire to escape hardship, but as a declaration of pure, selfless spiritual dedication. In this view, there is no wish to run away from work or to receive a physical reward. The slave longing for the shade represents serving without any expectation of a prize; rather, it is a pure desire to take shelter in the shadow of God, finding rest simply by being close to the Master. Likewise, the hired worker hoping for his reward does not express an expectation for a salary, but a deep anticipation for the action itself. Much like angels, the greatest desire of a righteous person is the actual service. As soon as he fulfills one commandment, he immediately hopes and yearns to perform another one just like it [אלשיך].