1)
What do we learn from "Lo Yidrechu"?
1.
Radak citing Midrash Shmuel 11:5: We find that Yisrael were more stringent about (they showed more than honor to) idolatry than Nochrim were. It says about Yisrael "Kol ha'Doleg 1 Al ha'Miftan" (Tzefanyah 1:9).
2.
Malbim: They thought that the victorious god was on the Miftan, and there [Dagon] bowed to it, therefore they honored the place.
1
Kli Yakar (Lani'ado): I.e. even the Kohanim would walk over it, just they would not step on the Miftan. Yisrael would not even walk over it; they would jump over it.