Regarding the word spoils, the Expositor's Commentary says that it literally means "the top of the heap," and is used of the choicest spoils of war. From these spoils, then, Abraham gave one-tenth - the very best - to Melchizedek. It is impossible to know how the spoils were laid out. Were all of the linens stacked together and the jewels in one chest and the armaments in a heap? Whatever the case, Abraham knew that his victory came from God, so he gave to God the very best that he had, the choicest spoils of the battle.
We must see and understand this attitude in giving. Why is Abraham called the "father of the faithful"? David is called a "man after God's own heart." Abraham, too, was a man after God's heart, but he is better known as the father of the faithful.
As we study tithing, a requisite that must be examined is our attitude. How do we approach God as we pay Him what we owe? Our money never seems to stretch far enough in this day and age. The world markets everything toward our lusts, and we feel that we have to have everything. Tithing often interferes with our desires. We can come to believe that God is keeping us from having what we want. Some come into the church up to their ears in debt and discover that they now must tithe on their incomes! They may feel that it is unfair, that undue pressure is being placed on them.
The problem with this thinking is that we are viewing the paying of tithes from the wrong perspective. The attitude of Abraham is an example for us as we give to God. We should wholeheartedly imitate his faithfulness as we, too, pay our tithes and give our offerings. God wants us to give a perfect offering to Him. This is really important! It should not become something that we just do, as if it were merely another bill to be paid.