Musar sur Téroumot 4:3

The patriarchs observed all the commandments as revealed later on in the Torah. We know from Genesis 14,20 that Abraham tithed when he gave the tithes to Malki Tzedek. In our פרשה we have a passage showing that Isaac also gave tithes; we know, of course, that Jacob promised to give tithes from his specific statement וכל אשר תתן לי עשר אעשרנו לך, “And all that You will give me, I will surely tithe to You" (Genesis 28,22). Our sages in Midrash Hagadol on that verse say that Jacob even tithed people. They explain that if we include Ephrayim and Menasseh in the count, there should have been fourteen tribes. Deduct four, seeing that each wife had a first born who was already sanctified from birth, and you remain with ten. From these remaining ten Jacob set aside Levi as a tithe to G–d. You see that all the patriarchs observed the commandment בכל לבבם, בכל נפשם ובכל מאודם, "with all their hearts, their souls and their means." The words בכל מאודם can be understood literally, i.e. "a tithe of everything." The expression בכל נפשם refers to Jacob who even tithed נפשות, people; the expression בכל לבבם, refers to תרומה גדולה, something for which the Torah does not prescribe a fixed amount. The amount to be set aside for the priest is left to the generosity of the individual, i.e. it is something to be decided on by his heart, לבבו. Our sages (Terumah 4,3) describe one fortieth as the תרומה of a generous individual, one fiftieth as the average gift, and one sixtieth as the תרומה of a miser. They derive these details from the verse in Genesis 14,20. It would have sufficed for the Torah to say ויתן מעשר, that Abraham tithed. Why did the Torah have to add the word מכל, from all? They answer that this is an allusion to תרומה מעשר, the tithe that the Levite has to give to the priest from the מעשר ראשון, the regular tithe that he received from the Israelite. I will explain later how this is alluded to in the text. Abraham gave to Malki Tzedek both the regular tithe and the תרומת מעשר. The numerical value of the letters in the word כל, all, is 50 which is an allusion to the 2% the average person sets aside. [In order to appreciate the following calculation, one must assume that Abraham first divided the entire harvest into two equal parts. This is not mentioned by the author. Ed.] Abraham removed one tenth of the total [taking it from one half] as tithe. He also set aside one part in fifty from the same total amount (before having tithed it) to give it separately as תרומה גדולה. When you remove "ten" from fifty, you are left with forty. This means that Abraham gave one part in forty as תרומה גדולה. [The normal procedure is to remove the תרומה גדולה from the harvest before measuring the ten per cent tithe from the remaining 98% of the harvest. Ed] Even though the normal or average amount set aside for תרומה is one in 50= כל, Abraham was more generous than that. All the patriarchs acted in a similar fashion.