Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

The money obtained from trespass-offerings and sin-offerings was not brought into the house of Jehovah, i.e., was not applied to the repairing of the temple, but was left for the priests. In the case of the trespass-offering compensation had to be made for the earthly debt according to the valuation of the priest, with the addition of a fifth in money; and this was assigned to the priests not only in the case of a מעל committed against Jehovah, but also when a neighbour had been injured in his property, if he had died in the meantime (see at Lev 5:16 and Num 5:9). On the other hand, in the case of the sin-offerings the priests received no money according to the law. Most of the commentators therefore assume, that those who lived at a distance had sent money to the priests, that they might offer sin-offerings with it, and what money as over they had retained for themselves. But there is not the slightest trace of any such custom, which is quite at variance with the idea of the sin-offering. It may probably have become a customary thing in the course of time, for those who presented these offerings to compensate the officiating priest for his trouble by a free-will gift.