Is the kippah a symbolic reminder intended to prevent assimilation, or is the kippah a biblical obligation like the tzitzit?
The tradition to wear a kippah is not derived from any biblical passage. Rather, it is a custom which evolved as a sign of our recognition that there is Someone “above” us who watches our every act.
The Talmud1 relates that a woman was once told by astrologers that her son is destined to be a thief. To prevent this from happening, she insisted that he always have his head covered to remind him of G‑d’s presence and instill within him the fear of Heaven. Once, while sitting under a palm tree, his head covering fell off. He was suddenly overcome by an urge to eat a fruit from the tree which did not belong to him. It was then that he realized the strong effect which the wearing of a kippah had on him.
In Talmudic times, the practice of wearing a head covering was reserved for men of great stature. In later generations, though, it became the accepted custom for all Jewish men to wear a kippah at all times, and especially during prayer. As with all Jewish customs, once they become a universally accepted Jewish practice, they become halachically obligatory.
According to some opinions, since wearing a kippah has become a form of distinction between Jews and non-Jews, failure to wear a head covering falls under the prohibition of “you shall not follow their statutes.”2
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1. Shabbat 156b.
2. Leviticus 18:3.
Article Source: chabad.org