The first 1/10th of our incomes belongs to God. We give this to the church to cover the costs of the work, booklets, Feasts, Sabbath services, feeding the flock, and warning the nations of the forthcoming Jacob's trouble.
Lev 27:30 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 to the LORD.
The second tithe is for the members to save for a year to pay for the Feast of Tabernacles. The costs of lodging, food and entertainment.
you shall spend that money for whatever your
heart desires: for oxen or sheep, for wine or
similar drink, for whatever your heart desires;
you shall eat there before the LORD your God,
and you shall rejoice, you and your household.