Dr. Martin Luther continues his commentary on Deuteronomy with this summary of chapter 14 – and it´s good reading about tithes, taxes and such laws and bylaws in this translation by Richard R. Caemmerer in Luther´s Works Volume 9, pages 138-141:

The Lord levied a threefold tithe upon this people. The one they gave once a year to the Levites, of all the fruits of the earth. The second they set apart every third year beyond that previously commanded, of all those same fruits of the earth, to be expended as though for a common chest and public alms—for the Levites and the strangers, the orphans and the widows; for He wanted no paupers to be in the land, as He says in the following chapter. Of these two tithes He speaks in this chapter. The third tithe was imposed upon the Levites, that of their tithes they would also give tithes to the priests; this is described in Leviticus. To these priests God also gave everything first-born, so that the first-born of men were redeemed with silver. Hence the ordinary income of the priests were the first-born or first fruits or tithes received from the Levites, to which were added the sacrifices and gifts of the whole people. The income of the Levites, however, were the tithes received from the people and part of the sacrifices, if they served the priests.

And would that all the other inequitable taxes were removed which today devour lands and people, and that tithes were instituted instead! If one were not sufficient, three, four, or five could be added. Thus a nation could live under its lords. This would be the most honorable and just method of income, for it would depend on the sheer goodness of God. If in a given year God were to bless richly, the people would have a rich yield, and the government rich tithes. But if He did not bless very much, the government would bear the burden equally with the subjects and would receive less. Now, however, since the annual taxes are fixed and certain and the bountiful years are few, the subjects are forced to pay the full taxes even if throughout a ten-year period or longer they do not have a single bountiful year. Yes, what is more pitiful, they are forced to pay the full taxes even if in that year they received from the land either hardly enough or not enough to pay what they owe; and this they do through a loan made elsewhere, which they use either to pay their taxes or to live on in that year.

Is this not worse than barbarity? Nay, is it not really a bestial and cruel greed? Do you, then, call these taxes just? Would you consider these laws equitable? No wonder the people are devoured and hounded from every place! What is the kingdom of Germany today but sheer tyranny? About foreign kingdoms I say nothing; I know nothing about them. I am concerned about our own. What prince or magistrate today do you think can be saved if knowingly or willingly he permits or does these things when, as a prince, he could and should help them to be otherwise? You see how little the cause of salvation impels princes here to work together in a common council, to act to the end that all taxes be wholly put away and changed into tithes (however many would be necessary), and to protect the people and rule the world with other laws. I admit, the common people are sunk in luxury and frivolity if they have plenty. But this situation should be improved by something else than unjust taxes, and a sin ought not be cured by a sin. Besides, the guilt of the corrupt people lies on the princes, who rule without law, without care, and without firmness, and strive only for taxes and lusts.

But let us return to Moses. Behold his excellent order of procedure! In the first place he deals with the yearly tithes and the yearly first-born, by which the priests and Levites are provided for. Then he deals with the triennial tithes, by which any poor are to be helped. Thus we are to understand that the ministers of the Word are to be provided for with primary concern; for through them not the belly but the heart and the spirit are fed. Then the bellies of the poor are to be cared for too. Therefore faith and the Word come before love and the good deed; and hence it is to be the first concern that faith and the Word are provided for rather than charity and the good work. But they are not provided for unless those who should teach are nourished. Yes, if faith and the Word perish, no love and good works will be left.

But law is law; men talk but do not act. For just as the people of Moses neglected this law and did not support its priests and Levites, so that these men were forced either to leave the Word and worship of God and take up some manual labor or to set up new doctrines and idolatries—for here the people richly supported its seducers and neglected the true shepherds, because they also turned away from the truth to fables—so it happens now too. No one supports the servants of the Word; for want of bread they are forced to leave the ministry and become farmers and ply trades, while the godless seducers have not only been fed but have filled the world with bishoprics and monasteries equal to the wealth of kings and princes. It is a just judgment of God that those who have not given and do not give to the minister of God and messenger of salvation one loaf of bread waste whole kingdoms and principalities on the servants of Satan and the messengers of death.

You see with what care St. Paul is concerned in 1 Cor. 9:7 ff.; 1 Tim. 5:17, Gal. 6:6, and elsewhere about the support of ministers of the Word. It is shameful for the great people of God to hear so many words regarding this very small matter from this great apostle. On the contrary, love ought so to flourish here that it would be necessary to restrain the people from giving, as in Ex. 36:5 ff.; according to the example of the Galatians, we ought (if it were possible) to pluck out our eyes for such ministers (Gal. 4:15). Hence, here, too—after he has spoken about tithes and the first-born—Moses adds: “That you may learn to fear the Lord your God always” (v. 23), namely, that to support the servants of the Word is the first and highest practice of the worship and fear of God. For how does he who fails in that support care for the Word of God? And how does he who does not care for the Word of God care for God? And he who does not care for God, how shall he fear God? Therefore to neglect and despise the servant of the Word is the same as to despise God and His Word. “He who hears you hears Me, and he who rejects you rejects Me” (Luke 10:16). This is what Moses impresses so carefully here and in so many other places: that they should not neglect the Levites, who have no other inheritance.