Leviticus 27:31

And if a man will at all redeem ought of his tithes, he shall add thereto the fifth part thereof.

The verse belongs to the system that consecrates one-tenth of a person's increase to God, covering field produce and livestock as well as the fruits of human labor. The tithe is the Lord's own holy property, and everything people have belongs to Him and is held only in trust to be faithfully returned to Him. It is His rental money for His vineyard.

If a person redeems or keeps for himself any part of the tithe, he must add a fifth part to its value, giving an equivalent plus the fifth, so its full value is not withheld. The statute was often repeated so that it would not be forgotten. Israel was to give God the first portion of the increase from flocks, herds, and fields, showing that His claims on income are to be met first and not postponed until other needs are satisfied.

The tenth is God's claim and the least that should be returned, so withholding any of it is robbery against God and calls for repentance for unfaithful dealing. All that people have, including physical and mental powers and capital of means, is only lent to them to be cultivated to bring large returns to God in tithes and offerings. A faithful tithe of all capital is required, with gifts and offerings in addition to the tithe, including a second tithe for the poor and other benevolent purposes.

A portion is set apart for sustaining the ministry to be used for no other purpose, while gifts and offerings meet the necessities of the church and the needs of the poor and suffering, given as a constant stream into the treasury so the work is not hindered. Keeping God's ownership before the people trains them to resist selfishness and to develop generosity and noble character. The requirement to add the fifth applies to unpaid back tithe, which is paid with the additional fifth.