Q. Why did Naomi tell Ruth to anoint herself?
As I explain in my study guide to Joshua, Judges, and Ruth, at the point in the book of Ruth that you’re asking about, Naomi was giving Ruth instructions that would signal to Boaz that the mourning period for Ruth’s late husband was now over and so Ruth was available for him to marry.
Naomi literally says “put your clothing upon you,” but by this she clearly means “your best clothing.” In other words, Ruth is to lay aside the widow’s garments she has been wearing, and instead put on something designed to be beautiful and attractive. Naomi also tells her to “anoint” herself. This means to put olive oil on her hair and head. This is still done in many similar climates and cultures to refresh the hair and skin. Some interpreters speculate that this could have been perfumed olive oil. If so, that would have been a further signal that Ruth was eligible for marriage.