(Numb. 5:15:) “Then he shall bring the offering for her, one-tenth an ephah of barley meal.” Why does she bring barley meal? Because she behaved in the manner of a beast with him, she therefore brings the food of a beast as her offering. (Ibid. cont.:) “He shall pour no oil upon it.”
Why does he not pour oil upon it? Because the oil is a light and is [also] called yitshar (a word which can mean "it will shine"); while this woman loves the darkness. Therefore there should be no light in her offering. [(Ibid., cont.:) Nor shall he put frankincense upon it.”] Why does he not put frankincense upon it?
Because the frankincense is a remembrance of the matriarchs, [as stated] (in Cant. 4:6), “I will go unto the mountain of myrrh and unto the mound of frankincense,” while this woman has withdrawn from their ways. Her offering should [therefore] be a reminder of iniquity and not a reminder of merit.