Why does a Jewish man cover his head? A person whose head is exposed stunts his spiritual growth, as the head covering has a positive, G-d-fearing effect on the person. As the Talmud says, “Cover your head so that you may be G-d fearing.” By covering the head, a person develops a strong sense of submission toward a Higher Being. It also increases awareness of his actions and reminds him that everything he does is revealed to the Creator, and that the world is not a place in which he is free to do anything he desires.
This is clearly seen among people who have a basic level of spiritual sensitivity and wear a kippah (skullcap) as a declaration of faith in the existence of a Creator. By doing so they’re also saying that they are the loyal subjects of the King of the world. This is included in the above mitzvah of sanctifying the Name of G-d.
This wonderful virtue of declaring one’s loyalty to a life of Torah and mitzvot through his outward appearance was brilliantly illustrated by the Rebbe of Slonim, zt”l:
Let us imagine a country in which some of its citizens had rebelled against the king. During that period, the citizens who remained loyal to the king decided to sew a piece of fabric onto the sleeves of their jackets that stated, “I am loyal to the king.” When the revolt is over, who will the king draw near him? Certainly those from the group that was not afraid to publicize their loyalty to him, especially at a time when there were others who rebelled against him.
The same goes for us. We are living in a time when many people are in violation of the King’s rule. Even though only a small group is acting this way intentionally while the vast majority is doing so unintentionally out of ignorance, there is nevertheless a certain quality of rebelliousness against G-d’s authority. But when a Jewish man walks down the street wearing a kippah (or a Jewish woman is dressed in a modest way), he is essentially making the following statement: “I am loyal to the King!” And who will the King draw near Him when His sovereignty is revealed in the times of the Messiah? Certainly those who were not afraid to publically declare that they were loyal to the King of the world during the rebellion.
Another matter related to the appearance of a Jewish man is the way in which he must maintain his hair and beard. We will discuss this at length in another article.
Notes and Sources
 Shabbat 156b. The following law is stated in the Shulchan Aruch (2:6) “One shall not walk four amot with his head uncovered.”