Sefer HaChinuch ספר החינוך

To not place olive oil in the meal-offering of a sinner: That a priest not place oil in the meal-offering of a poor sinner, as it is stated (Leviticus 5:11), “he shall not place oil on it” — and even though they would put oil on other meal-offerings. And I said, “the meal-offering of a poor sinner,” because of [the following]: since a rich sinner never brings a meal-offering of flour, but rather a sacrifice of a beast, as is explicit in the Torah.

It is from the roots of the commandment [that it is] because oil is a hint for stature and greatness — since if you mix it with any liquid, it floats above them all; and it is a very significant thing. And the significance of good oil is well-known — and therefore they would anoint those inaugurated to the stature of monarchy or priesthood with it. Hence it is not fit to place [some] of it in the meal-offering of the sinner who needs to show concern and lowliness about himself, that the matter of a sin came to his hand. And we can further say [it is] from compassion for the poor person, that he need not burden himself more than necessary to bring oil — as God, blessed be He, does not burden a creature. And because of this, it also obligated him only a little flour — as it is impossible for any person, even the most destitute of the destitute, [not to have] a little flour. And this will suffice for us also about the frankincense.

From the laws of the commandment is that which they, may their memory be blessed, explained (Menachot 76b) that the meal-offering of a sinner was one issaron — not less and not more. And all of the meal-offerings (Menachot 59a) offered on top of the altar require oil and frankincense. And [it is] one log of oil for one issaron of flour, and one handful of frankincense for any meal-offering — whether it was one issaron or sixty issaron, but we do not bring one meal-offering from more than sixty issaron — except for the meal-offering of jealousy and the meal-offering of the sinner, in which there is no oil or frankincense; as it is stated, “he shall not place oil on it, nor shall he put frankincense on it.” And the rest of its details are elucidated in Menachot.

And [it] is practiced at the time of the [Temple] by the males of the priesthood, as the service is theirs. And a priest that transgresses it and puts oil on this meal-offering of the poor sinner is lashed.