Kabbalah su Genesi 28:22

It appears to me, once we know that the previous tractate [ed. see introduction to Tractate Terumot above] corresponds to the 12 tribes, and also since it is well known that in all the Midrashim the Tribe of Levi is called "maaser" from the tribes (being as Jacob swore an oath to "give maaser from all that [God] gives me", he therefore separated Levi as "maaser"). Based on this, I feel forced to ask a question: In the Talmud, Tractate Ketubot (50a) teaches that a person should not give more than a fifth of his wealth to charity and brings a proof from Jacob who said "Aser Eh'asreinu" which the Talmud interprets to mean a fifth [ed. as opposed to merely a tenth as the simple reading implies]. If this is so, how could Jacob have fulfilled his oath by only sanctifying Levi [ed. which would be one tenth of his sons] when he vowed to sanctify one fifth [ed. ie. two children out of ten]?

When that time arrives, all the blessings will be aroused on all sides and the world will be properly established. From that day on, this kingdom shall rise, above all the other kingdoms, as was explained when discoursing on the verse, "but it shall break in pieces and consume all these kingdoms, and it shall stand forever" (Daniel 2:44). This is the stone that was cut out of the mountain and not by man, as it is written, "from thence from the shepherd, the Stone of Yisrael" (Beresheet 49:24). What is this stone? It is the congregation of Yisrael, as written, "and this stone, which I have set for a pillar..." (Beresheet 28:22).