It already said "va'Tashav mi'Sedei Mo'av" (6). Why does it say "va'Tetzei Min ha'Makom"?
Rashi: This teaches that when a Tzadik leaves a place, it makes an impression - its radiance, beauty and praise of the city left. The same applies to "va'Yetzei Yakov mi'Be'er Shava" (Bereishis 28:10).
Malbim: Regarding leaving, all of them were the same. All wanted to leave, for their Mazal was bad there. Initially, only Na'ami wanted to return to Eretz Yehudah; they wanted to live in Sedei Mo'av. Only after going on the road until the end of Eretz Mo'av - then the road is only to Eretz Yehudah - then also they agreed to return to Eretz Yehudah.
What do we learn from "va'Telachnah va'Derech Lashuv El Eretz Yehudah"?
Vilna Gaon: Initially, Na'ami thought that Rus and Orpah are going [only] to accompany her 1 . When she reached the crossroads and they went after her, she understood that they want to return with her to Eretz Yehudah.
Malbim: Refer to 1:7:1:2.
Malbim (8): Lest she go alone. She told them that she does not need an escort.
