Yod is the tenth letter and has the value ten. In size, it is the smallest of the letters, and the Talmud speaks of its bent head. Sefer Yetzirah places it in the group Gimel, Yod, Kaf, Kof, according to the place in the mouth that pronounces them. It is also the first letter of the divine Name, and the Talmud makes it, with Heh, one of the two letters through which the two worlds were created.
In Sefer Yetzirah, Yod is one of the twelve simples. G-d "made the letter Yod reign and bound a crown to it," and through it formed Betulah, the Virgin, in the world, the month of Elul in the year and the left kidney in the body. Yod is also the first of the three letters, Yod, Heh and Vav, with which G-d sealed the six directions of space.
In tractate Shabbat, the children's sentence nears its end: "if you do so, the Holy One, blessed be He, feeds you, is gracious to you, does good to you and gives you an inheritance." Yod gives yerushah, inheritance. What is given to the poor is not lost: it returns as a good that is passed on.
Tractate Menachot starts from a verse of Isaiah: "Trust in the Lord forever, for in Yah, the Lord, is the rock of the worlds." Rabbi Yehudah bar Ilai teaches that these are the two worlds G-d created, one through Heh, the other through Yod, and that the world to come was created through Yod. "Why was the world to come created through Yod? Because the righteous in it are few. And why is its head bent? Because the righteous in it have their heads bent, for their deeds are not like one another." The Alphabet of Rabbi Akiva reads Yod as yad, the "portion and name," yad vashem, that G-d will give the righteous in the world to come.
Ten, the small and the great. The smallest letter carries the world to come, and the Talmud reads its bent head as that of the righteous, each aware that his deeds are not like another's. Sefer Yetzirah makes it the first of the letters that seal space; the children of Shabbat 104a read in it inheritance. The smallest of the letters opens the Name and carries the world to come.