When Naomi describes her situation as “bitter” (Ruth 1:13, 20) she is like Israel in bondage, a slave in a foreign land (Ex. 1:14).
But if the bitter herbs of Passover are meant to recall that bitter service (12:8), then there is a kind of bitterness of heart before the Lord which is the prelude to freedom, the barrenness before fruitfulness (e.g. 1 Sam. 1:10).