B’resheet 14:18-20, talks of Malki-Tzedek and that Avram gave him a 10th of everything. 1 . What is this 10th and why was it given? 2 . Who is Malki-Tzedek? In Tehillim 110:4, it talks of Malki-Tzedek again and compares him to a Cohen. Why is this so? Who is v1-2 talking about?

His name Malkitzedek literally means, in Hebrew: my righteous king. In those days, before the ideals of separation and division of power, and separation of “church and state”, kingdom and priesthood usually went together. Shalem, his kingdom, is the original name of Jerusalem (Y’rushalayim, see the parallelism in Tehilim 76, 3, combined with the prefix “Y’re”, from Breishit 22, 14), and means “complete” or “peace”. According to some ancient sources in the midrash, Malkitzedek was a nickname for Shem, Noach’s righteous son, because he did a lot of kindness towards the animals on the ark (Shocher Tov 37, 1). Nevertheless, it’s difficult to ascertain whether a particular midrash is revealing an ancient traditional fact or whether it's coming to teach some philosophic, kabbalistic or esoteric idea. This 10% is the exact word (“Ma’aser”) and amount taken off for the Levi on regular crops in Israel to this day, and apparently he was seen as some form of priest (God obviously doesn’t need gifts, so all we can do, as if it were, to please or thank Him, is to tithe to some needy person). It’s important to note that in the original Hebrew, it’s unclear who is the giver and who the receiver, and some (e.g. Radak) explain that Malkitzedek (the regional king, superior to the kings of Sodom etc.) gave Avraham (!) that 10%, saying that one who toils to retrieve for his friend, deserves at least 10%! For if Avraham didn’t want to take the spoils for himself (which he recaptured from the 4 northern kings who took from Sodom and the 5 southern kings), wanting to return them to their original owner (Sodom, etc.), it’s illogical and maybe improper (although we don’t know all of the ancient customs) for him to give them to someone else (Malkitzedek). Malkitzedek is called a kohen in both Breishit and Tehilim, but in Tehilim, the context is that David and his heirs (also termed "Kohanim", see Shmuel II, 8, 18, for they are the national symbols and leaders of Israel, the Nation of Priests, Shmot 19, 6), the eternal kings of Y'rushalyim, are like a continuation of Malkitzedek. David and the future kings of Israel, are also the topic of verses 1-2, there.