The Philistine leaders stand completely helpless in the face of a severe disaster that struck them after capturing the Ark of the Covenant. In a desperate attempt to stop the suffering, they turn to their priests and diviners to find the exact way to appease God and atone for their actions.
They wonder how a person can physically return a sin or guilt. [מלבי״ם] explains that because the divine punishment perfectly matched their offense, the way to return the guilt is to recreate the exact shape of their plague, cast it in gold, and dedicate it to God. By doing this, they transform their symbol of rebellion and corruption into an object of honor and holiness.
The priests instruct them to prepare an offering that matches the number of Philistine leaders, specifically the five lords who ruled over the five major cities of Gaza, Ashdod, Ashkelon, Gath, and Ekron [רש״י]. The offering consists of five golden tumors, representing the painful sores that afflicted their bodies, and five golden mice, representing the vermin that overran them [מצודת ציון].
Commentators offer different perspectives on how the tumors and mice were connected. One approach suggests that the tumors themselves actually looked like mice, leading some doctors of the time to call the disease by that name [מצודת דוד, אברבנאל]. Another perspective views them as two entirely separate plagues: while the tumors physically attacked the people's bodies, the mice were an agricultural disaster that destroyed their crops [מלבי״ם, אברבנאל]. A third approach describes a horrifying reality where the two plagues combined. The disease caused the victims' intestines to protrude, and mice would then come and bite the exposed organs [רד״ק, אברבנאל].
The division of the offering into tumors and mice also reflects the social structure of the Philistines. The five large tumors represent the five ruling lords, while the five smaller mice represent the common people living under their authority, with each group bringing one mouse [מלבי״ם]. This distinction between the classes highlights how the lords and the commoners were traditionally viewed differently [אברבנאל].
Ultimately, the instructions conclude with the understanding that this was a single plague for everyone. The disaster equalized the entire population [מצודת ציון]. Because the plague did not distinguish between the common people and the leaders, every layer of society required atonement to the exact same degree [מצודת דוד, רד״ק]. The devastation was so absolute and widespread that it even afflicted the residents of cities where the Ark of the Covenant had never physically been taken [ביאור שטיינזלץ].