because He needs anything that He asks us to reserve a part of our possessions for Him.
The Lord created every tree in Eden pleasant to the eyes and good for food, and He bade Adam and Eve freely enjoy His bounties. But He made one exception. Of the tree of knowledge of good and evil they were not to eat. This tree God reserved as a constant reminder of His ownership of all. Thus He gave them opportunity to demonstrate their faith and trust in Him by their perfect obedience to His requirements.
So it is with God's claims upon us. He places His treasures in the hands of men, but requires that one tenth shall be faithfully laid aside for His work. He requires this portion to be placed in His treasury. It is to be rendered to Him as His own; it is sacred and is to be used for sacred purposes, for the support of those who carry the message of salvation to all parts of the world. He reserves this portion, that means may ever be flowing into His treasure house and that the light of truth may be carried to those who are nigh and those who are afar off. By faithfully obeying this requirement we acknowledge that all belongs to God.
And has not the Lord a right to demand this of us? Did He not give His only-begotten Son because He loved us and desired to save us from death? And shall not our gratitude offerings flow into His treasury to be drawn therefrom to advance His kingdom in the earth? Since God is the owner of all our goods, shall not gratitude to Him prompt us to make freewill offerings and thank offerings, thus acknowledging His ownership of soul, body, spirit, and property? Had God's plan been followed, means would now be flowing into His treasury; and funds to enable ministers to enter new fields, and workers to unite with ministers in lifting up the standard of truth in the dark places of the earth, would be abundant.