What tithe are we commanded to give to the Lord?
Key Verse:  Thou shalt truly tithe all the increase of thy seed, that the field bringeth forth year by year.  [Deuteronomy 14:22]
What is the law of tithing?

In order to promote the teaching and understanding of His commandments, God set in place a system of financial support for his work.  This financial system is called tithing.  All members of God's church are required to contribute a tenth part of their increase to the work of the church.

Thou shalt truly tithe all the increase of thy seed, that the field bringeth forth year by year.  [Deuteronomy 14:22]

And all the tithe of the land, whether of the seed of the land, or of the fruit of the tree, is the LORD'S: it is holy unto the LORD.  [Leviticus 27:30]

These specific instructions were given to the Children of Israel after they had been brought out of the land of Egypt.  However, the law of tithing predated the Children of Israel.

And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God.  And he blessed him, and said, Blessed be Abram of the most high God, possessor of heaven and earth:  And blessed be the most high God, which hath delivered thine enemies into thy hand. And he gave him tithes of all.  [Genesis 14:18-20]

For this Melchisedec, king of Salem, priest of the most high God, who met Abraham returning from the slaughter of the kings, and blessed him;  To whom also Abraham gave a tenth part of all; first being by interpretation King of righteousness, and after that also King of Salem, which is, King of peace;  [Hebrews 7:1-2]

And Jacob vowed a vow, saying, If God will be with me, and will keep me in this way that I go, and will give me bread to eat, and raiment to put on,  So that I come again to my father's house in peace; then shall the LORD be my God:  And this stone, which I have set for a pillar, shall be God's house: and of all that thou shalt give me I will surely give the tenth unto thee.  [Genesis 28:20-22]

We see in these verses that both Abraham and Jacob paid tithe, which was a tenth part of his increase.  The word tithe itself translates as "a tenth part". 

In olden times, tithes were paid directly from the goods which saw increase.  If a man's herd of cattle had twenty new calves born, then two cows were offered as tithe.  If two hundred measures of wheat were grown and gathered, then twenty measures were offered as tithe.  In our world today, most of our increase comes in the form of money earned from our jobs and various other sources.  Since our increase is measured in money, we tithe money.

In times of hardship, people may have difficulty paying their tithe.  God set in place a system by which his people may borrow against their tithe in order to get them through these hardships.  God allows us to delay the paying of our tithe in return for an addition fifth, or 20%.  If we borrow against our tithe, we must repay the original 10% plus an additional 20% of the 10%.

And if a man will at all redeem ought of his tithes, he shall add thereto the fifth part thereof.  [Leviticus 27:31]

The law of tithing is a commandment of God.  If we do not follow this commandment, we are stealing from God.

Will a man rob God? Yet ye have robbed me. But ye say, Wherein have we robbed thee? In tithes and offerings.  [Malachi 3:8]

Did Jesus do away with the law of tithing?

To answer this question we need to study the Priesthood under which we live.  When Jesus died for our sins on the cross, he did away with the "law contained in ordinances" or the "book of the law" and was established as a high priest after the order of Melchisedec.  The law that Jesus did away with was the added law that was given to the children of Israel under the Levitical priesthood because of transgression.  However the laws that were established under the Melchisedec priesthood before the Levitical laws were given still remain in effect today.  We know that the law of tithe was established under the Melchisedec preisthood because Abraham paid tithes hundreds of years before the Levitical laws were given.

And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God.  And he blessed him, and said, Blessed be Abram of the most high God, possessor of heaven and earth:  And blessed be the most high God, which hath delivered thine enemies into thy hand. And he gave him tithes of all.  [Genesis 14:18-20]

Because the law of tithing predates the giving of the Levitical law, we know that it is still in effect today as part of the Melchisedec priesthood.

Conclusion

Tithe is the means instituted by God for the financial support of His church.  Tithes are to be paid by all of his children, and these tithes are to be a tenth of our increase.  The law of tithing is in effect for us today and not paying this tithe is the same as stealing from God.