"All the silver and gold and the articles of bronze and iron are sacred to the Lord and must go into His treasury." - Joshua 6:19
One of the earliest examples of the practice of giving God the first fruits of the increase was when Joshua and the people entered the Promised Land for the first time. When they crossed the Jordan River, their first battle was Jericho. God set a precedent with this battle by instructing them not to take any spoils from it. Unlike future battles, the fruits from this victory were to go into the treasury as a remembrance of their first victory in the Promised Land. In addition, the city of Jericho was to be a lasting monument to God's faithfulness. God instructed Joshua never to rebuild this city. If they or anyone in the future attempted to rebuild the city, the life of the firstborn would be required. Years later in the days of King Ahab, Hiel the Bethelite attempted to rebuild this city and his firstborn died as a result. God never forgets to enforce His Word.
Is your work a lasting monument to the faithfulness of God in your life? Is it bringing glory to the Father? Are you giving the first fruits from your increase to God? God has encouraged us through this story to give the first fruits of our work to Him so that He will be glorified through our work. This is a tangible way for us to acknowledge that God is the source of all blessing.