John Calvin on Leviticus 27:30-33

30. And all the tithe of the land. In these words God shews that in assigning the tithes to the Levites, He ceded His own rights, inasmuch as they were a kind of royal revenue; and thus He bars all complaint, since otherwise the other tribes might have murmured on being unduly burdened. He therefore appoints the priests as His receivers, to collect in His name what could not be refused without impious and sacrilegious fraudulency. In the provision that, where the tithes are redeemed by a money payment, a fifth part should be added to their value, the object is not that the Levites should make a gain of the loss of others; but, because the owners of property craftily aimed at some advantage in this commutation of corn for money, frauds are thus prevented whereby something would be lost to the Levites by this deceptive exchange. On the same grounds He commands that the animals, whatever they might be, should be given as tithe, and does not permit them to be redeemed by money, since, if the choice had been free, no fat or healthy animal would have ever come to the Levites. Therefore, in this law a remedy was applied to avarice and meanness, and not without good cause; for if the proverb be true, that “good laws spring from evil habits,” See Tacitus Ann. 15:20. “Usu probatum est, patres conseripti, leges egregias, exempla honesta, apud bonos ex delictis aliorum gigni, etc." it was necessary that so covetous and ill-disposed a people should be restrained in the path of duty by the utmost severity. And although such careful provision was made for the Levites, yet there was scarcely any period in which they did not suffer from want, and sometimes they wandered about half-starved; nay, after the return from the Babylonish captivity, the memory of so great a blessing did not prevent a part of the tithes from being surreptitiously withheld from them; as God complains in Malachi 3:8. Whence it appears that it was not without purpose that the people were so imperiously enjoined to pay them.

Deuteronomy 14

Deuteronomy 14:22, 27-29

22. Thou shalt truly tithe all the increase of thy seed, that the field bringeth forth year by year.

22. Decimando decimabis omnem proventum seminis tui, quod egressum fuerit ex agro annuatim.

27. And the Levite that is within thy gates; thou shalt not forsake him; for he hath no part nor inheritance with thee.

27. Levitam autem qui intra portas tuas habitaverit non derelinques: quia non est ei pars et haereditas tecum.

28. At the end of three years thou shalt bring forth all the tithe of thine increase the same year, and shalt lay it up within thy gates:

28. Tertio autem anno proferes omnes decimas proventus tui anno ipso, et repones intra portas tuas.

29. And the Levite, (because he hath no part nor inheritance with thee,) and the stranger, and the fatherless, and the widow, which are within thy gates, shall come, and shall eat and be satisfied; that the LORD thy God may bless thee in all the work of thine hand which thou doest.

29. Venietque Levita (quia non est ei portio et haereditas tecum,) et peregrinus, et pupillus, atque vidua, qui sunt intra portas: et comedent, et saturabuntur, ut benedicat tibi Jehova Deus tuus in omni opere manus tuae quod feceris.