For the source text click/tap here: Menachot 41
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Generally speaking, there is no Biblical punishment for neglecting to perform a positive commandment; only transgressing negative commandments are grounds to be punished according to the Torah.
With regard to tzitzit it would appear that there should be no punishment if someone did not choose to wear them. In this context the Gemara relates the following story:
An angel once found Rav Ketina wearing a linen wrap, and he exclaimed, ‘Ketina, Ketina, a wrap in summer and a cloak in winter (apparently, neither of these had four corners, and so they were not obligated in tzitzit), and what is to happen to the law of tzitzit?’ ‘And do you punish’, asked Rav Ketina, ‘a person who neglects to perform a positive precept?’ ‘In a time of divine anger and judgment’, replied the angel, ‘we do’.
We explore divine anger in the bible.