We wear a kippah as a sign of respect and to remind us that G-d is watching over us..
The Kippah signifies our awareness and submission to the presence of the Holy One Blessed Be He.
The kippah has some powerful references in Talmudic literature, where it is associated with a sincere reverence for G-d.
In Kiddushin 31a - R. Honah Ben Joshua declares that he "never walked four cubits with his head uncovered . . . Because the Divine Presence is always over my head." Berachot 60b, it is written, "When he spreads a cloth upon his head he should say: Blessed are you (G-d) . . . Who crowns Israel with splendor."