Do you want to be blessed by G-d?
This is the key to blessing.
“Abraham’s nephew Lot had accompanied him to the Promised Land. Abraham was too idealistic for Lot, so Lot left him, settling near the Dead Sea. When the Land of Israel was later invaded by a coalition of nations who captured Lot, Abraham pursued them in his defense. After Abraham miraculously defeated the invaders, he gave a tenth of the spoils of war to his ancestor, Noah’s son Shem, who was then known as Malki-tzedek, king of Salem.
Tithing our wealth expresses our awareness that everything we possess really belongs to G‑d and must therefore be used for holy purposes. Generally, we amass wealth in order to improve our lives and the lives of our loved ones; the more we internalize the Torah’s values, the more these motives fuse with our desire to make the world more G‑dly.
However, when unearned wealth comes our way, it might not occur to us to relate to it in the same way. By tithing the spoils of war, which he received miraculously, Abraham demonstrated that not only the wealth that we have produced ourselves belongs to G‑d, but all our wealth.
G‑d promises to pay us back many times over for giving Him our tithes, and in fact implores us to test Him in this. By following Abraham’s example even with our unearned wealth, our lives will demonstrate how G‑d rewards those who fulfill His will. In this way, we, like Abraham, will disseminate the knowledge of G‑d’s goodness and kindness throughout the world.1 Likutei Sichot, vol. 5, pp. 68–76.