Commentaire sur Le Lévitique 5:11

כי חטאת הוא [HE SHALL PUT NO OIL UPON IT, NEITHER SHALL HE PUT ANY FRANKINCENSE THEREON:] FOR IT IS A SIN-OFFERING — a sinner’s offering, and therefore it is not proper that his offering should be embellished by oil and frankincense (Menachot 6a).

What is left of the bird may be eaten by the officiating priest. A commandment performed at its proper time is more welcome to the Lord than at a later time, i.e. the sinner having expected some substantial money coming his way and therefore preferring to wait with the sin offering until he can present an animal of greater worth. The same rule applies to the person who, although not even having sinned, promises his own worth as a donation to G-d shortly before reaching the age of twenty, at which time he must give the Temple treasury 50 shekels in order to discharge his vow as opposed to only 20 shekels.

כי חטאת היא, “for it really should have had the rules pertaining to a sin offering, requiring libations so that the sinner would not emerge as having actually profited. The reason why the Torah decided to forego this requirement is so that the sinner would not be able to boast about what kind of costly sacrifice he had brought in order to atone for what was, after all, only an inadvertent sin. In the case of someone who offers a sin offering for having been healed from the affliction of tzoraat, seeing that [at least according to the written text of the Torah, Ed.] He had not been afflicted for a specific sin that he had been guilty of, This offering is required only in order to enable the person offering it to be able to eat of sacrificial meat when the occasion arises. Therefore these offerings require libations, as our sages have stated in the Talmud tractate Sotah folio 36.