The braita explains that there is no way to test techelet (blue dye), and therefore one should only purchase it from an expert. Initially, the Gemara suggested this meant there was no way to distinguish between authentic techelet and kala ilan (a vegetable-based fake). However, this was rejected because there are indeed chemical tests available, as the Gemara explains. Ultimately, the conclusion is that there is no way to test if the strings were dyed "for the sake of the mitzva" (l'shma) or merely "for a tasting" (to test the color).

The Gemara then addresses: From whom may one buy tzitzit and assume they are valid? And why is it forbidden to sell tzitzit to a non-Jew?

There is also a dispute regarding whether tzitzit is a "time-bound positive commandment" (mitzvat aseh she'hazman grama). Rav Yehuda would place tzitzit on his wife's garments. However, Rabbi Shimon holds that it is time-bound and women are therefore exempt. The rabbis disagree with him, believing that nighttime is also a time for tzitzit. Rabbi Shimon derives from the words "And you shall see it" that the obligation only applies during the day. The Gemara brings many other drashot (interpretations) on this verse, most of which relate to the profound importance of the mitzva of tzitzit.

What is unique about the color techelet that this specific color was chosen for the mitzva? It serves as a reminder of the heavenly throne.