The bond between God and the Israelites was meant to be as intimate and constant as a piece of clothing clinging to a person's body. Just as a belt wraps tightly around the waist and goes everywhere with its wearer, God desired to draw the nation to Himself in an inseparable, close relationship. The primary approach among commentators is that this belt serves as a sweeping metaphor for the entire history and purpose of the nation, with every detail of its story reflecting a specific phase of their journey.
The act of purchasing the belt represents how God acquired the Israelites, proving His ownership by bringing them out of Egypt through miraculous signs and wonders [מלבי״ם, אברבנאל]. The specific choice of a linen belt points to their growth and expansion, as they transformed from a despised group of slaves into a massive nation. Furthermore, the instruction to keep the belt away from water serves as a reminder of the miraculous crossings of the Red Sea and the Jordan River on completely dry land [אברבנאל].
God envisioned four distinct dimensions of purpose and closeness for the nation, all mirroring the characteristics of a finely crafted belt. The foundation of this bond was their status as His acquired people, showing that God chose them for His own personal purpose [מלבי״ם]. Beyond this, just as an elegant belt brings attention and high status to the person wearing it, the relationship was intended to grant the Israelites a great reputation [מצודת דוד, מלבי״ם, ביאור שטיינזלץ]. It was also meant to generate praise, allowing the nation to radiate power and heroism [מצודת ציון, מלבי״ם, ביאור שטיינזלץ]. Finally, the bond was designed for splendor, reflecting the physical beauty of the linen and the elevated standing of the people [מלבי״ם, ביאור שטיינזלץ]. Ultimately, this intense closeness was designed to reflect praise and splendor back onto God Himself [אברבנאל].
However, this vision ended in complete tragedy. The people refused to listen to God and actively rejected this tight bond [מצודת דוד, ביאור שטיינזלץ]. This stubborn refusal to listen also parallels the earlier instruction to avoid putting the belt in water [מלבי״ם]. Because they severed this connection, the nation suffered the exact same fate as the physical belt. Just as the belt was removed from the waist, hidden in the rocky crevices near the Euphrates River, and left to rot, the Israelites faced a similar ruin. Taking the belt to the Euphrates represents the people being exiled from the land of Israel. The moment they stepped outside their borders and broke away from God's guidance and closeness, they lost their core purpose. In exile, they became entirely useless and corrupted, exactly like a ruined belt rotting away in the earth [אברבנאל, ביאור שטיינזלץ].