Doctrine and Covenants 119-120

How does faithfully paying tithing purify your heart and prepare you to live in a Zion society?

Revelation given through Joseph Smith the Prophet, at Far West, Missouri, July 8, 1838, in answer to his supplication: “O Lord! Show unto thy servants how much thou requirest of the properties of thy people for a tithing.” The law of tithing, as understood today, had not been given to the Church previous to this revelation. The term tithing in the prayer just quoted and in previous revelations (64:23; 85:3; 97:11) had meant not just one-tenth, but all free-will offerings, or contributions, to the Church funds. The Lord had previously given to the Church the law of consecration and stewardship of property, which members (chiefly the leading elders) entered into by a covenant that was to be everlasting. Because of failure on the part of many to abide by this covenant, the Lord withdrew it for a time and gave instead the law of tithing to the whole Church. The Prophet asked the Lord how much of their property He required for sacred purposes. The answer was this revelation.

1–5, The Saints are to pay their surplus property and then give, as tithing, one-tenth of their interest annually; 6–7, Such a course will sanctify the land of Zion.

1 Verily, thus saith the Lord, I require all their surplus property to be put into the hands of the bishop of my church in Zion,

2 For the building of mine house, and for the laying of the foundation of Zion and for the priesthood, and for the debts of the Presidency of my Church.

3 And this shall be the beginning of the tithing of my people.

4 And after that, those who have thus been tithed shall pay one-tenth of all their interest annually; and this shall be a standing law unto them forever, for my holy priesthood, saith the Lord.

5 Verily I say unto you, it shall come to pass that all those who gather unto the land of Zion shall be tithed of their surplus properties, and shall observe this law, or they shall not be found worthy to abide among you.

6 And I say unto you, if my people observe not this law, to keep it holy, and by this law sanctify the land of Zion unto me, that my statutes and my judgments may be kept thereon, that it may be most holy, behold, verily I say unto you, it shall not be a land of Zion unto you.

7 And this shall be an ensample unto all the stakes of Zion. Even so. Amen." (Doctrine and Covenants 119)

"Revelation given through Joseph Smith the Prophet, at Far West, Missouri, July 8, 1838, making known the disposition of the properties tithed as named in the preceding revelation, section 119.

1 Verily, thus saith the Lord, the time is now come, that it shall be disposed of by a council, composed of the First Presidency of my Church, and of the bishop and his council, and by my high council; and by mine own voice unto them, saith the Lord. Even so. Amen." (Doctrine and Covenants 120)

And here's the beginning part of the commentary entitled: "My tithing helps build the kingdom of God." :

"The instructions in sections 119 and 120 clarify what tithing is: we contribute “one-tenth” of our interest (or income) each year (see Doctrine and Covenants 119:4). But these revelations do more than give a definition. The Lord told the Saints that tithing would “sanctify the land of Zion.” And without this law, He said, “it shall not be … Zion unto you” (verse 6). Have you ever thought about tithing in this way? How can paying tithing help make you more sanctified, more prepared for Zion?

What do you learn from these revelations about how the Lord’s servants use tithing funds? What is significant to you about the phrase “by mine own voice unto them” in Doctrine and Covenants 120?"

Zion is the pure in heart. Paying tithing makes me more sanctified, more prepared for Zion because it purifies my heart's desire by making me put God first and give back to Him the 10% of my income to help in building His kingdom, before spending and/or saving 90% for my own needs and wants. Sacrificing a part of my income rather than using 100% is giving me the opportunity to give of what I have received and think not only of myself, instead think of how I can contribute to building up the Lord's kingdom. 

The significance of the phrase "by mine own voice unto them" to me is that the Lord is involved as His servants make decisions on how to use tithing funds?