Ruth in Central Africa: A Cultural Commentary (Ruth 3:3)

Naomi’s instructions to Ruth sound very out of character for a God-fearing “mother” — to actually teach her daughter how to make herself attractive so that she can go out and entice men in the practice of prostitution! In this context it would seem as if Naomi is encouraging Ruth to carry on as a harlot so that she can earn enough money to support the two of them. It would be difficult to think of a more immoral proposition. The careful instructions about the need for secrecy as well as the time of action — at night (v. 2) and after the man had finished eating and drinking (the latter bearing a certain negative connotation in itself) — would serve to confirm this suspicion.
So would the advice to “lie down” at his feet under his blanket (v. 4). This was apparently (since we have this as the only clear instance [but note Ezek. 16:8]) a culturally symbolic act which was intended to dramatize for Boaz the responsibility that he had to protect, care for, and possibly even marry, Ruth. It is difficult to remove from the text the suggestion that sexual relations, and an illicit encounter at that, were a part of this rather elaborate procedure. An explanatory footnote is therefore necessary at this point.

Source: Wendland 1987, p. 177f.