Hashem commanded Bnei Yisrael to tie tzitzit to the corners of their four-cornered garments as a reminder to fulfill the mitzvos and not stray after the desires of their hearts and eyes. The mitzvah consists of a tassel — a group of threads known collectively as “tzitzit” — to four corners of any garment that has four corners or more, and to wind a blue-colored thread (techelet) around the top part of each set of fringes. The bottom part of the tassel and the remaining thread of techelet are left loose. The Torah explains that this mitzvah of tzitzit helps the people fulfill all of the mitzvos. By looking at them, they would “remember all of Hashem’s commandments and thereby be prompted to perform them.” This in turn would prevent them from straying “after [their] hearts and eyes” (Bamidbar 15:39).
How does looking at tzitzit serve as a reminder? In ancient times it was customary for a master to place an emblem on his servant’s clothing as a sign that he belonged to him. Similarly, tzitzit are Hashem’s “emblem” that Bnei Yisrael are His servants. Indeed, He took them out of Egypt on condition that they serve Him, and they agreed with a solemn oath. Thus, whenever Bnei Yisrael see their tzitzit they remind themselves that they are Hashem’s servants and therefore are not at liberty to simply do as they please.
This also explains why Hashem specifically commanded Bnei Yisrael to attach tzitzit to clothing. There is no better reminder than attaching an emblem to clothing, since it is in front of the wearer the entire day. Furthermore, the techelet thread, which is dyed using the blood of a rare sea creature called a “chilazon,” has a color similar to the color of the sea, and the color of the sea is similar to that of the sky, which in turn is similar to the color of Hashem’s Throne of Glory. Thus, by looking at the blue thread, a person remembers He who sits upon the throne.
Even without the chilazon dye, the mitzvah can still be performed with plain white strings. As Rashi explains, even without the techelet thread, there is an allusion to the 613 mitzvos in the tzitzit. The word tzitzit (spelled with two yuds) has a numerical value of 600. Add to this eight and five (eight hanging strings and five knots), and we have 613.
By looking at their tzitzit and having a constant reminder of Hashem and His mitzvos, following the Sin of the Spies, Bnei Yisrael would now be able to resist the desires that tempt them to stray from Hashem’s service. Moreover, the injunction not to stray after the desires of the heart and eyes comprises a separate mitzvah, one that is applicable at all times, even when one is not wearing tzitzit.
Hashem promised Bnei Yisrael that if they fulfill the mitzvah of tzitzit they would “become holy.” Some commentators understand that performing the mitzvah of tzitzit alone brings a person to holiness, while the Midrash explains that through the mitzvah of tzitzit, one performs all the mitzvos and this makes him holy.
The passage of tzitzit provides the means to prevent Bnei Yisrael from committing a similar sin to the sin of the Spies by warning the nation not to stray after their hearts and eyes, and since tzitzit serves as a constant reminder of all the mitzvos, it provides a way to elevate the nation and help them remain forever conscious of their duties. The verses include a promise that if the nation performs all of Hashem’s mitzvos, then it will “become holy” and “be a kingdom of priests and a holy nation.”.