And their redemption price (at a month old you shall redeem them) you shall fix at five shekels in silver, according to the shekel of the sanctuary, which is twenty gerahs.
The priest's service is called a warfare; and who goes a warfare at his own charges? As they were well employed, so they were well provided for, and well paid. None shall serve God for nought. All believers are spiritual priests, and God has promised to take care of them; they shall dwell in the land, and verily they shall be fed, and shall not want any good thing.
Commenting on Numbers 18:8-19
But the firstling of a cow, or the firstling of a sheep, or the firstling of a goat, thou shalt not redeem,.... That is, shalt not take the redemption price for them, but the creatures themselves; which they, the priests, were to take for their own use: they are holy; separated to the Lord, and therefore not to be used in common by men, but...
THE PRIESTS' PORTION. (Num 18:8-20) the Lord spake unto Aaron, Behold, I also have given thee the charge of my heave offerings--A recapitulation is made in this passage of certain perquisites specially appropriated to the maintenance of the priests. They were parts of the votive and freewill offerings, including both meat and bread, wine and oil, and the first-fruits, which formed a large and valuable item.
Commenting on Numbers 18:8-20