The Sisit, as we know, is tied in five knots on each corner of the garment, and the strings then hang down beneath the series of knots. The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933), in Siman 11, writes that the five knots allude to the five books of the Humash, which we are to bear in mind when we view the Sisit.
Furthermore, the Mishna Berura adds, each of the five knots is tied twice, into a double knot, such that there are actually ten knots on each corner of the garment. The Mishna Berura writes that these ten knots are symbolic of the ten Sefirot (“filters”) through which the Almighty’s presence comes into this world – Hochma, Bina, Da’at, Hesed, Gebura, Tiferet, Nesah, Hod, Yesod and Malchut. The knots of the Sisit thus bring to mind the five books of the Torah and the ten Sefirot through which G-d is manifest in the world.