Tithe  empowers the denomination. There would be no administrative apparatus comparable to the existing one, without tithe. 

Every third year, tithe of the produce was for the levite,widow, alien, and orphan (Deut. 14:27,28).

The tithe was to be consumed by the people paying it (Deut. 14:22-27).

Every 7th year was a Sabbath; therefore, no tithe.

EGW explains that there were actually two tithes required (PP ch. 51). 25%, not 10%, was required of them (PP 527)

Note the following summary from the Jewish Encyclopedia s.v. tithe: "It is to be concluded that, the seventh year being a Sabbatical year and no tithing being permissible therein, the tithe of the first, second, fourth, and fifth years of every cycle of seven years had to be brought to the Temple and eaten by the landowner and his family, while the tithe of the third and sixth years was to be left at home for the poor." 

Tithe was paid long before Moses by both Abraham and Jacob (Gen. 14:20; 28:22).