The Israelites stand at a crossroads, making a final, resolute choice about their spiritual future. Their declaration of loyalty to God rests on a direct connection between His historical actions and their ongoing commitment to Him. They recognize the kindness and love God showed by walking with them and guiding them, concluding that abandoning Him now is simply impossible [ביאור שטיינזלץ].
Their answer is a logical and direct response to the options Joshua presented earlier. When challenged to choose between the gods of Egypt or the gods of the Amorites, the people firmly reject both. It makes no sense to worship the gods of the Amorites, since God drove the Amorite nation out before them. Likewise, there is no reason to serve the gods of Egypt, as God already saved them from Egyptian control [מלבי״ם].
Furthermore, the Israelites understand the severe consequences of living in their new home. They know that if they adopt the practices of the expelled nations, the land will expel them exactly as it did to the nations that preceded them [מלבי״ם]. Against this backdrop, the nation makes a unified pledge, accepting the responsibility to serve God with the exact same dedication that Joshua promised for himself and his own family [מצודת דוד].