Aleph and Tav being the first and the last letters of the alphabet, th — Aleph

"And when he desired to create the world, all the letters came in turn and each said to the Holy One, blessed be He: Lord of the Universe, may it be Your will that the world be created through me. ... When aleph saw that the Holy One, blessed be He, desired to create the world through bet, she stood to one side and was silent, until the Holy One, blessed be He, called her and said to her: aleph, why are you silent; why do you not speak as your companions? Aleph answered and said before Him: Lord of the Universe, My companions amount to much, but I am of little value. The Holy One, blessed be He, said to her: No wonder that you are the first and the sovereign, since I am One and you are one. Since you have been humble, I will glorify you by making you a thousand (elef)."

"The only letter that had refrained from urging its claims was the modest Alef, and God rewarded it later for its humility by giving it the first place in the Decalogue."

"Some claim to find a satisfactory explanation of the origin of this letter in that it represents an ox-yoke, or the head of an Ox, the horns forming the top part of the letter. This is highly significant, for the letter when pronounced as Aleph and spelt in full h, means an Ox or Bull, an admirable symbol to denote the generative power of Nature."