The word tithe comes from the Old Testament principle of a tenth—giving a tenth. Actually, going back to Leviticus one of the feasts was a feast of first fruits, which has the same idea that the first fruits you gather we want to honor God because He is the one who provided the fruit in the first place. So, we want to return that and honor God and worship him by giving back a tenth to him. The principle of tenth goes all the way back to Abraham when he brought a tithe to Melchizedek, 10%. So that principle has been running throughout Scripture.
With regard to whether it is commanded or not. In the New Testament, there really is nothing where a tithe is commanded. But certainly, giving generously back to the Lord, to His work and His kingdom, is clear. Paul, in 1 Corinthians 8, speaks about giving back abundantly to the Lord.
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