And we make known to you concerning all the priests, etc. This privilege, by which priests, Levites, and the other ministers of the house of God are rendered free from taxes, is clearly shown, in that the rest of the people of the children of Israel, upon arriving in the homeland, paid tribute to the king. This is known to be done by the king with well-considered provision, so that those who were always occupied in divine service might be free from their servitude; and those who possessed nothing of their own on earth, but lived from the tithes of the people, from these no one should demand the payment of tributes. From all these things, it is most clearly proven that the king not only loved, but also very well learned what the worship of divine service required.
Source: Commentary on Ezra and Nehemiah