“tithe, yes, tithe.” This is the figure of speech polyptoton, where the word “tithe” is repeated twice in the Hebrew text, but the two occurrences are inflected differently. The double use of “tithe” is for emphasis, which some translations express by saying something such as, “You are to surely tithe.”
[For more on the use of polyptoton, and the translation of it, see commentary on Gen. 2:16.]
The Law of Moses commanded people to give a tenth of the grain they grew and the other vegetable harvests such as grapes and olives (Lev. 27:30; Num. 18:21; Deut. 14:22; Mal. 3:8-12). Animals were tithed also, but differently (Lev. 27:32). There was no formal tithe in the over 2500 years from Adam to the Mosaic Law. The reason for the institution of the tithe was that God commanded that the tribe of Levi could not own land and was to do the work of the Temple, as well as other duties that required their attention. As long as the people of the other 11 tribes of Israel paid their tithe, there was money for the Levites. When the Law of Moses was fulfilled and the physical Temple was no longer the true Temple, the tithe was no longer a legal requirement (the Body of Christ is the Temple today—see commentary on 1 Cor. 3:16).
Since there is no legal requirement to give a tenth today, the Bible says that Christians are to give as they purpose in their heart (2 Cor. 9:7). However, they are still to give, and giving generously is always God’s heart. Christians are to give to those who minister the Word of God within the Body of Christ (1 Cor. 9:11-14). They are also to give to those in need (cp. Phil. 4:10-14), and are to keep in mind that those who sow generously will reap a generous reward for it (2 Cor. 9:6).