יואל, פרק ג׳, פסוק ד׳

As the ultimate day of God approaches, the natural world will undergo intense transformations, particularly in the skies. These celestial shifts carry deep physical, symbolic, and spiritual meaning. The darkening of the sun is understood in several ways. On a natural level, it may refer to a solar eclipse [אבן עזרא], or a state where the sun is completely hidden from view [ביאור שטיינזלץ]. Alternatively, the darkness could be the result of thick smoke and raging fires rising from the intense heat of that time [מלבי"ם]. Beyond the physical realm, this event serves a spiritual purpose, meant to shame those who bow down and worship the sun as a deity [רש"י]. Others view this imagery purely as a metaphor. Because of the overwhelming distress and hardship that will fall upon humanity, people will feel as though the daylight itself has faded away [מצודת דוד].

Similarly, the moon shifting its color to red is seen as either a lunar eclipse [אבן עזרא] or a rare atmospheric phenomenon [ביאור שטיינזלץ]. Yet, this visual change holds a darker meaning. The moon, which naturally represents moisture and water, taking on the appearance of blood acts as a severe warning. It signals upcoming wars, widespread killings, fires, and destruction that will lead to the death of many nations [אבן עזרא, מלבי"ם]. Once again, this can also be understood as a poetic way to describe a period of deep trouble, where the moon simply fails to provide its usual comforting light [מצודת דוד].

All these events are set to take place right before the arrival of God's great and terrible day. This time is recognized as the ultimate day of judgment [מלבי"ם], or the period immediately preceding the final redemption [מצודת דוד]. It is called great and terrible because it is the moment when the sheer magnitude of God's rule and His awe-inspiring actions will be openly revealed to everyone [מצודת דוד].