ישעיהו, פרק מ׳, פסוק ד׳

As the exiled Israelites prepare to return to their homeland, they are promised a perfectly smooth, straight, and comfortable journey. The prophet does not merely issue a call to prepare the way; he declares a firm promise that this will actually happen in the future [שד״ל]. The primary approach among commentators is that this dramatic reshaping of the landscape serves as a metaphor for an effortless journey. In the natural world, climbing up and down mountains causes great exhaustion for travelers. However, those returning from exile will experience no fatigue at all [רד״ק, אבן עזרא, צאינה וראינה, שטיינזלץ].

To create this perfectly level path, every low valley will be raised up, while every mountain and hill will be brought down. One unique perspective highlights the miraculous and supernatural nature of this process. Normally, when people level a road, they take dirt from a mountain and use it to fill in a valley. In this promised future, however, the valley will miraculously rise on its own, and only afterward will the mountain sink [מלבי״ם].

Beyond merely leveling the heights and depths, the path itself will be completely transformed. Any crooked, twisted, or winding roads will be straightened into flat, even ground [מצודות, רד״ק, אבן עזרא, שטיינזלץ]. Furthermore, the rough terrain will be smoothed out into a wide plain. Most commentators understand these rough areas to be high spots and bumps along the road [מצודות, רד״ק, אבן עזרא]. Alternatively, others explain that these refer to mountain ranges that are tightly connected. Such clustered mountains typically create steep, difficult slopes that force travelers to take long, tiring detours [רש״י, מלבי״ם]. Ultimately, all of these topographic obstacles will be entirely removed, transforming into a smooth, wide, and flat plain so that absolutely nothing will delay the returning Israelites on their journey [רש״י, שטיינזלץ].