Rabbi Yoshiyah tackled a question about the scope of the commandment of first fruits, bikkurim. (Deuteronomy 26:2) commands, "Then you shall take of all the fruits of the earth." Read broadly, this could mean the entire land — all territories conquered and settled by Israel. But Rabbi Yoshiyah argued the obligation was narrower.
His method was gezerah shavah, the rabbinic technique of linking passages through shared language. In (Exodus 13:5), which names the five nations whose land God swore to give the patriarchs, the text uses the word "swearing." In (Deuteronomy 26:3), part of the first fruits declaration, the same word "swearing" appears: "the land which the Lord swore to our forefathers to give us."
Because both passages share the verb "swearing," Rabbi Yoshiyah concluded they refer to the same territory — the land of the five nations listed in Exodus, not the full seven. This means that the obligation to bring bikkurim applied only to produce grown in the territories of these five nations, not to land conquered beyond those original boundaries.
The practical consequence was significant. Territories east of the Jordan or lands captured in later expansions would not generate an obligation for first fruits. The holiness of the bikkurim offering was tied specifically to the land that God swore to Abraham, Isaac, and Jacob — the core inheritance, not the extended empire.