The tithing system reaches back beyond the days of Moses. Men were required to offer to God gifts for religious purposes before the definite system was given to Moses, even as far back as the days of Adam. In complying with God's requirements, they were to manifest in offerings their appreciation of His mercies and blessings to them. This was continued through successive generations, and was carried out by Abraham, who gave tithes to Melchizedek, the priest of the most high God. CS 69.1
The same principle existed in the days of Job. Jacob, when at Bethel, an exile and penniless wanderer, lay down at night, solitary and alone, with a rock for his pillow, and there promised the Lord, “Of all that Thou shalt give me I will surely give the tenth unto Thee.” God does not compel men to give. All that they give must be voluntary. He will not have His treasury replenished with unwilling offerings.—Testimonies for the Church 3:393. CS 69.2