וַתֹּאמַ֖רְנָה־לָּ֑הּ כִּי־אִתָּ֥ךְ נָשׁ֖וּב לְעַמֵּֽךְ׃
און זײ האָבן צו איר געזאָגט: נײן, נײַערט מיר װעלן מיט דיר זיך אומקערן צו דײַן פֿאָלק.
Ralbag Ruth
"Because with you we will return to your people" — meaning, they will not separate from her people, who are Israel, and therefore they will return with her even though she has no sons. It seems that they converted when Mahlon and Chilion married them, which is why we do not find that Ruth needed to convert when Boaz married her. For this reason, they were also returning with her. This is why they said, "Because with you we will return to your people." However, Naomi wanted to test if they had converted out of love for God or if they had converted due to their desire for her sons.