ישעיהו, פרק מ׳, פסוק ל׳

Human physical strength, even at the very peak of vitality, is inherently limited. When a person relies solely on their own power, that strength will eventually betray them [שטיינזלץ]. While this reality applies to human nature in general, where strong young people inevitably grow tired and fail [אבן עזרא], the primary approach among commentators reads this as a powerful metaphor. The imagery of vigorous youth represents the wicked nations of the world, idol worshippers, and the enemies of Israel, such as the Chaldeans. These empires appear to grow stronger and more dominant every day. However, their power is an illusion; the moment God decides, their might will vanish, and they will collapse [רד״ק, מצודת דוד, צאינה וראינה]. Building on this spiritual layer, some explain that the concept of youth here actually implies an inner emptiness, describing individuals who are completely void of God's commandments [רש״י, צאינה וראינה].

There are different ways to understand the progression of this downfall. Some view the descriptions of tiring and stumbling as a simple repetition meant to emphasize the same underlying idea [מצודת דוד]. Others, however, see a precise sequence of decline. Younger, less experienced individuals grow weary naturally, either on their own or through physical effort. In contrast, the more mature and robust young men do not tire from natural exertion. Therefore, when they collapse, it is not due to ordinary fatigue. Instead, their sudden downfall is caused by an external force directly sent by God [מלבי״ם].

At its core, the concept of stumbling represents a fundamental physical weakness. Just as weak knees inevitably lead to a fall, or a hidden obstacle causes a person to trip [שד״ל], those who place absolute trust in their own might are destined to collapse. This creates a sharp contrast: those who rely on personal power will ultimately fail, whereas those who place their hope in God will be granted entirely new strength [רש״י, מלבי״ם].