G‑d then instructed Moses regarding the laws of three commandments that are deemed equivalent to observing the entire Torah: not worshipping idols, observing the Sabbath, and wearing tassels (tzitzit) on the corners of four-cornered garments. The numerical value of the Hebrew word tzitzit is 600; when this number is added to the number of half-threads (8) and knots (5) in each tassel, the sum is 613, the number of commandments in the Torah.
Remembering the Source
וּרְאִיתֶם אֹתוֹ וּזְכַרְתֶּם אֶת כָּל מִצְוֹת ה' וַעֲשִׂיתֶם אֹתָם וגו': (במדבר טו:לט)
[G‑d instructed Moses to tell the people,] “When you see [the tassels], you will remember all the commandments of G‑d, in order to perform them.” Numbers 15"39

Granted that we need the tassels to remind us of the 613 commandments, but why do we need the garment to which the tassels are attached? Why not just carry the tassels themselves?

The answer lies in the significance of garments. The difference between clothing and food – our two main necessities – is that food becomes a part of us when we eat it, while clothing always remains outside of us. Food therefore alludes to the aspects of the Torah that we can comprehend and “digest,” while clothing alludes to that which remains beyond our grasp.

The instruction to attach the tassels to a garment indicates that it is not sufficient simply to remember the commandments. Wearing such a garment helps us remember that the Torah and its commandments originate in G‑d’s wisdom, which transcends the limitations of human intellect.1