Rashi says Korach gathered two hundred and fifty of the leaders of Bnai Yisroel and dressed them in Talaisim that were made out of Techales, he stood them before Moshe and asked if a Tallis is made completely out of Techales - does it still need Tzizis? Moshe replied it needs Tzizis Korach and his followers began laughing - if a garment made out of other material one string of Techales is enough - so a garment made completely out of Techales should not need the string of Techales. We know that the reason for the string of Techales (blue) is to remind us of the heavens and the heavenly throne. So Korach’s question made a lot of sense. If one string is sufficient to serve as a reminder, an entire garment should surely be sufficient without adding the Tzizis. The Torah gives us the reason for many of the Mitzvos. For other Mitzvos, we can logically develop the reasons. Korach’s mistake was that he assumed that if the reason no longer exists, the Mitzvah ceases to exist. On the contrary. The Mitzvah exists - reason or not. We are obligated to perform the Mitzvah because the Torah commands us to. (Rabbi Moshe Feinstein)
