The first fruits is recognition of God’s Lordship over all things. When someone returns his first fruit, he is in fact recognising that God is Lord, not only Lord of his life but also Lord of everything his life produces. The deepest meaning of tithe is that everything (100 percent) belongs to God.
When we give Him the first fruits (10 percent of everything), it is to release the remaining 90 percent for our use. In other words: everything belongs to God; we give Him 10 percent in order for us to have the privilege of using the other 90 percent.
The Lord said, “If I were hungry, I would not tell you; for the world is Mine, and all its fullness. Will I eat the flesh of bulls, Or drink the blood of goats? Offer to God thanksgiving, and pay your vows to the Most High. Call upon Me in the day of trouble; I will deliver you, and you shall glorify Me.” (Psalms 50.12-15)
In other words, God makes it clear that if He needed money, He would not ask us because He owns everything! But if we pay our vows and offer thanksgiving to Him, then He will be pleased and also will answer us when we call upon Him in the day of trouble.
Among the Jews, the tithe signified their recognition of God’s participation in their productivity. The purpose of the first fruits was not to consecrate the harvest, but to ‘de-consecrate’ it. For everything belonged to God until the first portion, the first fruits, had been offered and accepted in place of the whole (100 percent).
Only then, man could use the other 90 percent for himself. The first fruits represents God’s own firstborn, Jesus Christ, the Son of the Most High, who was given by God to mankind, to redeem him to Himself.
That’s the reason why we must return the first fruits.